JP4929751B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  2. Description of the Related Art In recent years, an image forming apparatus that includes a sheet conveying unit that conveys a sheet and an image forming unit that forms an image on the conveyed sheet has been widely used as a printer or a copying machine. In such an image forming apparatus, the position in the width direction perpendicular to the conveyance direction of the paper conveyed by the paper conveyance unit and the position where the image is formed in the image formation unit are aligned, so that an appropriate position of the paper is obtained. An image is formed.

For example, in Patent Documents 1 and 2, a paper position sensor that measures the position in the width direction of a paper is provided in the paper transport unit, and an image formed by the image forming unit is based on the position measured by the paper position sensor. An image forming apparatus for adjusting the position is shown. Here, the paper position sensor is arranged upstream of the registration roll in the paper transport direction so that the measured paper position information is in time for the start of image formation. According to these image forming apparatuses, the position for forming an image on the paper is adjusted based on the position of the paper on the upstream side of the registration roll. Also, the skew of the paper is corrected by the paper being abutted against the registration roll.
JP 2002-292960 A Japanese Patent Laid-Open No. 3-119375

  However, in the image forming apparatuses disclosed in Patent Documents 1 and 2, the paper whose position in the width direction is measured by the paper position sensor is then positioned in the width direction when it abuts against the registration roll and the skew is corrected. May shift. As a result, an image whose position is adjusted based on the measured position of the sheet may actually be formed at a position shifted from the sheet.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus in which the displacement of the position of an image formed on a sheet is suppressed.

The first image forming apparatus of the present invention that achieves the above object forms an image on a conveyed sheet, and an image forming section capable of adjusting an image forming position in a width direction perpendicular to the sheet conveying direction. And a paper transport unit for transporting paper on a paper transport path passing through the image forming unit,
The paper transport unit is
It is composed of a pair of rolls arranged in contact with each other to form a nip area, which is disposed upstream of the image forming unit in the paper conveyance direction. In addition, a registration roll that sends the paper to the image forming unit in accordance with the timing of image formation in the image forming unit,
A first sensor that is provided between the registration roll and the image forming unit and measures the position in the width direction of the first sheet that has been conveyed this time toward the image forming unit;
A position information storage unit that stores position information of the first sheet in the width direction based on the measurement result of the first sensor;
The image forming unit adjusts the image forming position in the width direction of an image to be formed on the second sheet conveyed from the next time on the basis of the position information stored in the position information storage unit. It is characterized by being.

  The positional deviation in the width direction of the paper transported by the paper transport unit occurs while the paper is transported from the paper tray along the paper transport path. For this reason, the position of the conveyed paper in the width direction varies greatly depending on the individual image forming apparatus and paper tray, but when viewed as a combination of a certain image forming apparatus and paper tray, The variation of the position for each conveyed sheet is relatively small. This also applies to the skew of the sheet, and therefore, the variation for each sheet with respect to the position in the width direction of the sheet after the skew is corrected by the registration roll is relatively small. In the first image forming apparatus of the present invention, the image forming position with respect to the sheet conveyed after the next time is adjusted based on the measurement result of the position of the sheet after the skew is corrected. Shift of the image position is suppressed.

In the first image forming apparatus of the present invention, the first sensor is a paper sensor that detects the presence or absence of paper,
It is preferable that the image forming apparatus includes a moving unit that moves the paper sensor in the width direction.

  By using a paper sensor having a simple configuration for detecting the presence or absence of paper, the cost of parts can be reduced.

  Further, in the first image forming apparatus of the present invention, the image forming unit conveys the first sheet by the sheet conveying unit after the type of the sheet conveyed by the sheet conveying unit is changed. In the case of the first sheet, the image forming position in the width direction of the image formed on the first sheet is determined based on an initial value determined in advance according to the type of the first sheet. It is preferable to adjust.

  Since the position of the transported paper in the width direction and the degree of misalignment due to skew correction differ depending on the paper type, when the transported paper type is changed, it was obtained from the previous type of paper. When the image forming position is adjusted based on the position information, the position where the image is formed becomes inappropriate. In this case, an image is formed at a position based on a predetermined initial value.

The second image forming apparatus of the present invention that achieves the above object forms an image on the conveyed paper, and the image forming position can be adjusted in the width direction perpendicular to the paper transport direction. A forming unit, and a sheet conveying unit that conveys a sheet on a sheet conveying path passing through the image forming unit,
The paper transport unit is
It is composed of a pair of rolls arranged in contact with each other to form a nip area, which is disposed upstream of the image forming unit in the paper conveyance direction. In addition, a registration roll that sends the paper to the image forming unit in accordance with the timing of image formation in the image forming unit,
A first sensor that is provided between the registration roll and the image forming unit and measures the position in the width direction of the first sheet that has been conveyed this time toward the image forming unit;
A second sensor that is disposed upstream of the registration roll in the transport direction and that measures the position in the width direction of the first paper transported this time toward the registration roll;
The position of the first sheet in the width direction at the measurement position of the first sensor is estimated based on the measurement result of the second sensor and the predetermined parameter of the first sheet conveyed this time. A position estimation unit for obtaining a position estimated value;
A parameter calculation unit that calculates a parameter for obtaining a position estimated value that matches a position measurement value obtained by measuring the position of the first sheet in the width direction with the first sensor;
A parameter storage unit that stores parameters calculated by the parameter calculation unit,
When the position estimation unit obtains a position estimation value for the second sheet conveyed from the next time onward, it is stored in the parameter storage unit and the measurement result of the second sheet by the second sensor. A position estimation value for the second sheet is obtained by estimating the position in the width direction of the second sheet based on
The image forming unit adjusts the image forming position in the width direction of an image formed on the second sheet based on the position estimated value of the second sheet obtained by the signal estimating unit. It is characterized by being.

  In the second image forming apparatus of the present invention, the position of the first sheet before skew correction by the registration roll is measured by the second sensor, and the skew correction of the first sheet is corrected based on the measurement result. A position estimate is estimated. The measurement of the position of the first sheet is also performed after the skew correction by the first sensor, and a parameter in which the position estimated value and the position measured value match is calculated and stored. For the second sheet conveyed after the next time, the position estimation value after skew correction is estimated using the measurement result of the position before skew correction and the stored parameters. Therefore, in the second image forming apparatus of the present invention, the measurement result of the position before skew correction and the parameter adjusted based on the actual measurement of the first sheet for the second sheet conveyed from the next time onward. Thus, the estimated position value after the skew correction is estimated, and the image forming position is adjusted based on the estimated position value, so that the deviation of the position of the image formed on the sheet is suppressed.

In the second image forming apparatus of the present invention, the second sensor measures the position in the width direction of the paper being transported at a plurality of locations in the transport direction of the paper.
The position estimation unit determines the first sheet at the measurement position of the first sensor based on the measurement result of the second sensor at a plurality of positions of the first sheet and a predetermined parameter. In estimating the position in the width direction to obtain a position estimated value and obtaining the position estimated value for the second sheet conveyed from the next time onward, the second position at a plurality of positions on the second sheet is obtained. The position of the second sheet in the width direction is estimated based on the measurement result of the sensor and the parameters stored in the parameter storage unit, and the position estimated value for the second sheet is obtained. Preferably there is.

  By measuring the position of the paper before skew correction at a plurality of positions and using it for estimation, a highly accurate position estimation value reflecting the state of the skew before skew correction is estimated. Therefore, the displacement of the position of the image formed on the paper is further suppressed.

In the second image forming apparatus of the present invention, each of the first sensor and the second sensor is a first paper sensor and a second paper sensor that detect the presence or absence of paper,
The image forming apparatus may include a first moving unit and a second moving unit that move the first paper sensor and the second paper sensor in the width direction.

  Further, in the second image forming apparatus of the present invention, the position estimating unit conveys the first sheet by the sheet conveying unit after the type of the sheet conveyed by the sheet conveying unit is changed. In the case of the first sheet that has been produced, the first sheet is measured based on the measurement result of the first sheet by the second sensor and an initial value that is predetermined according to the type of the first sheet. It is preferable that the position estimated value is obtained by estimating the position in the width direction of the first sheet at the measurement position of one sensor.

  The degree of skew in the transported paper and the amount of misalignment associated with skew correction differ depending on the paper type, so when the transported paper type was changed, it was obtained from the previous type of paper. When the image forming position is adjusted based on the parameters, the image is formed at an inappropriate position. In this case, the position estimated value is obtained based on a predetermined initial value.

  Here, the first sensor may measure the position in the width direction of the sheet conveyed toward the image forming unit at a plurality of positions in the conveyance direction of the sheet.

  The paper may remain skewed even after skew correction by the registration roll. By measuring the position of the paper at a plurality of positions after the skew correction, the paper position can be obtained more accurately.

  Further, the image forming unit and the sheet conveying unit are configured such that a difference in the position in the width direction at a plurality of positions of the sheet conveyed toward the image forming unit measured by the first sensor is a predetermined threshold value. If it exceeds, the operation may be stopped.

  If the skew of the paper is too large, the image cannot be formed normally and there is a possibility of paper jam, so it is necessary to stop the operation. However, the position of the paper at a plurality of positions by the first sensor is measured. By using the result, it is possible to easily determine whether to stop the operation.

  Further, the image forming unit is predetermined according to the type of the sheet when the type of the sheet conveyed by the sheet conveying unit is changed and the first sheet is conveyed after the sheet type is changed. The image forming position in the width direction of the image formed on the sheet may be adjusted based on the initial value.

  In the first sheet after the sheet type is changed, the information based on the measured value for the preceding sheet is meaningless, but even in this case, it is based on the predetermined initial value. An image is formed at the position.

  As described above, according to the present invention, an image forming apparatus in which a shift in the position of an image formed on a sheet is suppressed is realized.

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

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

  An image forming apparatus 1 shown in FIG. 1 corresponds to the first image forming apparatus of the present invention, and controls the operations of the image forming mechanism 10, the paper transport mechanism 20, and the entire image forming apparatus 1. Control unit 30 and two trays 40 (40a, 40b) for storing paper.

  The image forming mechanism 10 forms an image on a sheet by electrophotography, and includes a scanner 11, a photosensitive drum 12, a charger 13 for uniformly charging the photosensitive drum 12, and an electrostatic latent image as a toner image. A developing unit 14 for developing, a transfer unit 15 for transferring a toner image onto a sheet, and a cleaner 16 for collecting residual toner that has not been transferred are provided.

  An image signal transmitted from the outside is converted into a signal by exposure light in a laser output unit 11a included in the scanner 11, and rotates through a polygon mirror 11b, an fθ lens 11c, and a reflection lens 11d. An electrostatic latent image based on the image signal is formed on the drum 12. The electrostatic latent image is formed by the scanner 11 scanning the surface of the photosensitive drum 12 with exposure light in the direction of the rotation axis of the photosensitive drum 12. The scanner 11 starts exposure at the adjusted exposure start timing, and forms an electrostatic latent image by scanning the surface of the photosensitive drum 12 with exposure light at a specified scanning speed. The electrostatic latent image is developed by the developing unit 14 to obtain a toner image. The toner image is transferred by the transfer unit 15 to the sheet conveyed through the sheet conveyance path R. Thereafter, the toner is removed from the photosensitive drum 12 by the cleaner 16 and is charged by the charger 13.

  Since the scanning direction by the scanner 11 coincides with the paper width direction perpendicular to the paper conveyance direction, the position of the image formed by the image forming mechanism 10 in the paper width direction starts scanning by the scanner 11. The timing is controlled so that it can be adjusted freely.

  The paper transport mechanism 20 includes transport rolls 24 and 25 that transport the paper stored in the tray 40 along a paper transport path R that passes through the image forming mechanism 10, and a registration roll 21. The registration roll 21 is disposed upstream of the image forming mechanism 10 in the sheet conveyance direction, and includes a pair of rolls that contact each other to form the nip region 21a. The sheet conveyed by the conveyance roll 24 is abutted against the nip region 21a of the registration roll 21, so that the skew of the sheet, that is, the skew state is corrected. In addition, the registration roll 21 sends the paper to the transfer unit 15 of the image forming mechanism 10 in accordance with the timing of image formation in the image forming mechanism 10.

  The paper transport mechanism 20 includes a first edge sensor 22 that measures the position in the width direction of the paper transported toward the image forming mechanism 10, a registration roll 21, and a transfer unit 15 of the image forming mechanism 10. Between.

  The control unit 30 receives signals from each sensor of the image forming apparatus 1 including the first edge sensor 22 and controls the operation of each part mechanism of the image forming apparatus 1. Although the function of the control unit 30 will be described later, for example, the position of the image formed on the paper by the image forming mechanism 10 is adjusted by controlling the timing of the scanning start by the scanner 11. Although not shown, the control unit 30 controls the overall operation of the image forming system based on a program, a ROM that stores programs and tables, and a temporary storage area in the CPU. It has a RAM to be provided and an interface circuit that relays signals between the outside of the control unit 30 and the CPU. Various functions provided by the control unit 30 are realized based on programs executed by the CPU.

  FIG. 2 is a diagram showing an appearance of the first edge sensor shown in FIG.

  As shown in part (a) of FIG. 2, the first edge sensor 22 includes an arm 221 that moves in a direction perpendicular to the paper transport direction, and a motor 222 that moves the arm 221. As shown in part (b) of FIG. 2, a first paper sensor 225 including a light emitting diode 224 and an optical sensor such as a photodiode is provided at the front end of the arm 221. It is attached toward one point.

  The arm 221 is driven by a motor 222 under the control of the control unit 30 and moves in a direction perpendicular to the paper transport direction. The presence or absence of a sheet at the position of the first sheet sensor 225 is detected based on whether or not the light emitted from the light emitting diode 224 is reflected by the sheet and reaches the first sheet sensor 225. The control unit 30 controls the first edge sensor 22 to cause the first edge sensor 22 to measure the position of the side edge that is one side parallel to the paper transport direction. Hereinafter, the side edge position of the sheet will be described as a position perpendicular to the sheet conveyance direction. The first paper sensor 225 corresponds to an example of a first sensor according to the present invention, and the arm 221 and the motor 222 that move the first paper sensor 225 correspond to an example of a moving unit according to the present invention.

  The sensor for measuring the position of the paper is not limited to the combination of the paper sensor for detecting the presence or absence of the paper and the arm. For example, a line sensor constituted by a photodiode array, a CCD (Charge Couple Device), or the like is used. It may be used. However, by using the first paper sensor 225 having a simple configuration for detecting the presence or absence of paper, the cost of parts can be reduced.

  FIG. 3 is a functional block diagram of the image forming apparatus 1 shown in FIG.

  The control unit 30 includes a scanning control unit 31, a mechanism control unit 32, a conveyance control unit 33, an image position adjustment unit 34, a corrected edge position measurement unit 35, and a position information storage unit 36. A personal computer (PC) 50 is externally connected to the control unit 30.

  The post-correction edge position measurement unit 35 drives the motor 222 of the first edge sensor 22 and detects a signal from the first paper sensor 225, whereby the first paper sensor 225 receives the image forming mechanism from the registration roll 21. The side edge position of the sheet conveyed toward 10 is measured. The post-correction edge position measurement unit 35 stores position information representing the side edge position L of the sheet as a measurement result in the position information storage unit 36.

  The position information based on the measurement result for the sheet is temporarily stored in the position information storage unit 36 and used for the position prediction of the next sheet to be conveyed. Here, the information once stored in the position information storage unit 36 is added with “(n−1)” in order to indicate that it is information about the paper that has been transported earlier in time. .

  The image position adjustment unit 34 reads the position information stored in the position information storage unit 36, and on the sheet conveyed from the next time on the basis of the side edge position L (n-1) represented by the read position information. The image forming position M in the width direction of the image to be formed is adjusted. The image forming position M in the width direction of the image is obtained by adding a predetermined margin width to the value of the side edge position L (n−1) of the sheet. The image position adjusting unit 34 also stores an initial value of position information for the first sheet after the change when the type of the sheet on which the image is formed is changed. As the initial value, a standard side edge position value determined according to each size of the paper is set.

  The scanning control unit 31 controls the operations of the laser output unit 11a and the polygon mirror 11b of the scanner 11 according to the image signal transmitted from the personal computer 50. At this time, the scanning control unit 31 controls the output start timing of the laser output unit 11a and the rotation phase of the polygon mirror 11b based on the image forming position M, thereby changing the scanning start timing by the scanner 11 and changing the image. The position in the width direction of the image formed by the forming mechanism 10 is set to the image forming position M adjusted by the image position adjusting unit 34.

  The mechanism control unit 32 controls operations of the image forming mechanisms 12 to 17 including the respective units of the image forming mechanism 10 except the scanner 11.

  The conveyance control unit 33 controls the operation of the paper conveyance mechanism 20 including the registration roll 21. For example, the transport control unit 33 sets the paper tray of the paper to be transported by the paper transport mechanism 20 between the tray 40b and the tray 40a in accordance with the paper type information transmitted from the personal computer 50 along with the image signal. Switch. As a result, the type of paper conveyed by the paper conveyance mechanism 20 is changed.

  The combination of the image forming mechanism 10, the scanning control unit 31, the mechanism control unit 32, and the image position adjusting unit 34 of the present embodiment corresponds to an example of the image forming unit of the present invention. The combination of the paper transport mechanism 20, the transport control unit 33, the corrected edge position measurement unit 35, and the position information storage unit 36 corresponds to an example of the paper transport unit of the present invention.

  FIG. 4 is a diagram illustrating a state in which an image is formed on a sheet by the image forming apparatus illustrated in FIG.

  In FIG. 4, the transport roll 24, the registration roll 21, and the photosensitive drum 12 are shown together with the sheets P1 and P2 on which images are formed. Note that the transport roll 24, the registration roll 21, and the photosensitive drum 12 are shown at intervals for easy viewing of the drawing.

  Here, the operation of the image forming apparatus 1 will be described with reference to FIGS.

  In FIG. 4, the toner image formed on the photosensitive drum 12 is transferred to the first paper P1, so that the image is formed on the first paper P1, and the second paper P2 is A state in which the sheet is conveyed toward the registration roll 21 by the conveyance roll 24 is shown.

  The skew of the first sheet P1 has been corrected by being already abutted against the registration roll 21 at the time of FIG. Further, after the skew is corrected, the conveyance control unit 33 causes the registration roll 21 to send the first sheet P1 to the transfer unit 15, so that an image is displayed on the first sheet P1 as shown in FIG. Will be formed. Since the timing at which the registration roll 21 feeds the first sheet P1 to the transfer unit 15 is synchronized with the timing at which the electrostatic latent image is formed on the photosensitive drum 12 by the scanning control unit 31, the image Q is It is formed at an appropriate position in the transport direction Y of the first paper P1.

  The scanning control unit 31 causes the scanner 11 to scan the surface of the photoconductor drum 12 with exposure light in the paper width direction K, thereby forming an electrostatic latent image corresponding to the first paper P1 on the surface of the photoconductor drum 12. . The electrostatic latent image formed on the photosensitive drum 12 is developed with toner to become a toner image, and is transferred onto the first sheet P1 by the transfer unit 15. The scanning control unit 31 controls the scanning start timing of the scanner 11 to start scanning from the image forming position M on the photosensitive drum 12. As a result, the image Q is formed at the image forming position M in the width direction X of the first sheet P1.

  The first paper sensor 225 receives the control of the corrected edge position measurement unit 35, and after a predetermined time has elapsed since the registration roll 21 sent the first paper P1, the side edge position L of the first paper P1. Measure. The measurement result of the side edge position L of the paper P1 after the skew is corrected is stored in the position information storage unit 36 by the corrected edge position measurement unit 35 as position information.

  On the other hand, the skew of the second paper P2 is corrected by being abutted against the registration roll 21 by the transport roll 24 (P2 '). Thereafter, the second sheet P <b> 2 ′ is sent to the image forming mechanism 10 by the registration roll 21. In synchronization with this, an electrostatic latent image corresponding to the second sheet P2 'is formed on the photosensitive drum 12. Here, prior to the formation of the electrostatic latent image corresponding to the second sheet P <b> 2 ′, the image position adjustment unit 34 reads the position information stored in the position information storage unit 36. The read position information represents the side edge position L of the first sheet P1, and the image position adjustment unit 34 adds a predetermined margin width to the value of the side edge position L to determine the image forming position M. calculate. The scanning control unit 31 controls the scanning start timing of the scanner 11 based on the calculation result of the image forming position M by the image position adjusting unit 34 and starts scanning with the exposure light from the image forming position M. Therefore, the next image is formed at the image forming position M in the width direction X of the second sheet P2.

  Here, the shift of the side edge position of the paper transported toward the registration roll 21 occurs while the paper is transported from the paper tray along the paper transport path, so the first transported sequentially. The difference in side edge position is relatively small between the second sheet P1 and the second sheet P2. This also applies to the skew of the sheet. Therefore, the skew is corrected by the registration roll 21, and the side edge position L of the first sheet P1 sequentially fed to the image forming mechanism 10 and the first skew are sent. The difference from the side edge position L of the second sheet P2 is small. According to the image forming apparatus 1 of the first embodiment, the image forming position M with respect to the second sheet P2 conveyed from the next time is measured on the side edge position L of the sheet after correcting the skew of the first sheet P1. Since the adjustment is made based on the result, the displacement of the position of the image formed on the sheet is suppressed.

  As described above, the side edge position after correcting the skew of the paper sequentially conveyed by the image forming mechanism 10 is approximated if the paper type is the same, but if the paper type is different, the skew degree is different. The degree of misalignment associated with skew correction is different. Therefore, for example, when the first sheet P1 is the first sheet after the change of the sheet type, the adjustment of the image forming position M for the sheet P1 is stored in the position information storage unit 36, and the pre-change is performed. If it is performed based on the position information obtained from the type of paper, the image is formed at an inappropriate position. When the first sheet P1 is the first sheet after the change of the sheet type, the image position adjustment unit 34 calculates the image forming position M based on an initial value determined in advance according to the sheet type. As a result, an image is formed at a position based on the initial value for the first paper P1 after the change of the paper type.

  Next, a second embodiment of the present invention will be described. In the following description of the second embodiment, the same reference numerals are given to the same elements as those in the embodiments described so far, and differences from the above-described embodiments will be described.

  FIG. 5 is a schematic configuration diagram of an image forming apparatus according to the second embodiment of the present invention.

  The image forming apparatus 2 shown in FIG. 5 corresponds to the second image forming apparatus of the present invention, and includes a second edge sensor 63 disposed on the upstream side of the registration roll 21 in the transport direction. And the configuration of the control unit 60 are different from those of the image forming apparatus 1 of the first embodiment.

  The second edge sensor 63 has the same configuration as that of the first edge sensor 22 shown in FIG. 2, and includes a second paper sensor 635 serving as a second sensor, a motor 632 (see FIG. 6) serving as a moving unit, and an arm. It has. The second sheet sensor 635 measures the side edge position of the sheet conveyed from the conveyance roll 24 toward the registration roll 21 in accordance with control from the control unit 60. In the present embodiment, the second paper sensor 635 measures the side edge position at two locations in the paper transport direction.

  FIG. 6 is a functional block diagram of the image forming apparatus 2 shown in FIG.

  The control unit 60 includes a scanning control unit 31, a mechanism control unit 32, a conveyance control unit 33, an image position adjustment unit 66, and a corrected edge position measurement unit 35. In addition to these, a parameter storage unit 65 is further provided. A pre-correction edge position measurement unit 61, a position estimation unit 62, and a parameter calculation unit 64.

  The pre-correction edge position measurement unit 61 drives the motor 632 of the second edge sensor 63 and receives a signal from the second paper sensor 635, thereby conveying the second paper sensor 635 toward the registration roll 21. The side edge positions L1 and L2 (see FIG. 9) of the sheet before skew correction that has been performed are measured. The second paper sensor 635 reciprocates at a predetermined timing while the paper passes through the position of the second paper sensor 635 on the conveyance path, so that the side at two predetermined positions in the paper conveyance direction of the paper. Edge positions L1 and L2 are measured.

  The position estimation unit 62 detects the position of the sheet whose position is measured by the second sheet sensor 635 of the second edge sensor 63 when the sheet is conveyed to the position where the first sheet sensor 225 of the first edge sensor 22 is installed after skew correction. The side edge position of is estimated. The value estimated by the position estimating unit 62 is assumed to be a position estimated value L0 (see FIG. 9). The position estimation unit 62 determines the position estimation value L0 based on the side edge positions L1 and L2 measured by the second paper sensor 635 and the correlation parameter K described later under the control of the pre-correction edge position measurement unit 61. calculate.

  The parameter calculation unit 64 uses the side edge positions L1 and L2 whose positions are measured by the second sheet sensor 635, and the registration roll 21 of the sheet that is actually measured by the first sheet sensor 225 of the first edge sensor 22. The correlation parameter K is calculated based on the side edge position measurement value L after passing. Specifically, a correlation parameter K for causing the position estimation unit 62 to match the position estimation value L0 obtained based on the side edge positions L1 and L2 with the side edge position measurement value L is calculated. A detailed method for calculating the correlation parameter K will be described later. The parameter calculation unit 64 stores the calculated correlation parameter K in the parameter storage unit 65.

  The position estimation unit 62 described above calculates the position estimation value L0 based on the side edge positions L1 and L2 measured by the second edge sensor 63 and the correlation parameter K. When obtaining the estimated position value L0 for the conveyed sheet, the correlation parameter K stored in the parameter storage unit 65 is read, and the estimated position value L0 is calculated based on the read correlation parameter K. A specific method for calculating the position estimated value L0 will be described later. The position estimation unit 62 stores an initial value of the correlation parameter K for the first sheet after the change when the type of the sheet on which the image is formed is changed. As the initial value, a correlation parameter value expected in the design stage of the image forming apparatus or a correlation parameter value obtained by transporting a sample paper in a shipping test is set according to each size of the paper. Yes. The position estimation unit 62 adjusts the image forming position M for the first sheet after the change of the sheet type based on the initial value corresponding to the sheet type. Since the degree of skew in the paper and the degree of misalignment due to skew correction differ depending on the type of paper, the position estimation unit 62 performs the first change after changing the paper type when the type of paper being conveyed is changed. For the paper, the estimated position value L0 is adjusted based on the initial value corresponding to the paper type.

  The image position adjustment unit 66 is based on the estimated position L0 of the sheet at the installation position of the first edge sensor 22 by the position estimation unit 62, and the image in the width direction of the image formed on the second sheet. The formation position M is adjusted.

  The combination of the image forming mechanism 10, the scanning control unit 31, the mechanism control unit 32, and the image position adjusting unit 66 of the present embodiment corresponds to an example of the image forming unit of the present invention. The combination of the paper transport mechanism 20, the transport control unit 33, the corrected edge position measurement unit 35, and the position information storage unit 36 corresponds to an example of the paper transport unit of the present invention.

  FIG. 7 is a diagram illustrating a state in which an image is formed on a sheet by the image forming apparatus illustrated in FIG.

  FIG. 7 corresponds to FIG. 4 in the first embodiment, but with respect to FIG. 4, a second edge sensor including a second paper sensor 635 on the upstream side in the transport direction Y with respect to the registration roll 21. 63, and a sheet sensor 68 for detecting the passage of the sheet is disposed in the vicinity of the second edge sensor 63 on the conveyance path. When the paper sensor 68 detects the passage of the paper, the second edge sensor 63 follows the control of the pre-correction edge position measurement unit 61 and is conveyed toward the registration roll 21 to the side edge of the paper before skew correction. Positions L1 and L2 (see FIG. 9) are measured. The side edge position is measured at two locations in the paper transport direction Y by the second paper sensor 635 of the second edge sensor 63.

  FIG. 8 is a diagram for explaining the measurement of the side edge position of the sheet by the second edge sensor.

  In FIG. 8, the vertical axis indicates the passage of time, and the horizontal axis indicates the position of the second edge sensor 63 in the direction perpendicular to the sheet conveyance direction of the second sheet sensor 635. In FIG. 8, with the passage of time, when the plurality of sheets P11, P12, P13, P14, and P15 are conveyed in this order by the conveying roll 24 (FIG. 7), the second sheet sensor 635 is sequentially activated. A state of measuring the side edge position is shown. Actually, the second paper sensor 635 of the second edge sensor 63 is fixed in the paper transport direction and moves the paper. However, in the figure, for convenience of explanation, the second paper sensor 635 is fixed with the paper position fixed. The paper sensor 635 is shown to scan over the paper in the paper transport direction.

  For example, the second paper sensor 635 first moves to a home position out of the paper transport path at time t1. When the paper P11 is transported by the transport roll 24 at time t2, the second paper sensor 635 moves to a standby position corresponding to the size of the paper P11, and at time t3, the paper sensor 68 (FIG. 7) moves to the paper P11. Is detected, the sheet moves toward the center of the sheet conveyance path in the sheet width direction. At this time, the first side edge position L1 is measured by passing the side edge of the paper P11. Further, at time t4 after a predetermined time has elapsed, the second paper sensor 635, on the contrary, measures the second side edge position L2 while moving toward the standby position. In this way, by controlling the movement timing of the second paper sensor 635 in accordance with the conveyance of the sheet, the side edge position at a specific position in the sheet conveyance direction is measured. Similarly, for the papers P12 and P13 following the paper P11, the side edge positions are measured at two locations while reciprocating. Thereafter, when the paper type is switched and the paper size is changed, the second paper sensor 635 moves to a standby position corresponding to the newly changed paper size (time t7), and reciprocates from this standby position. Measure the side edge position while moving. In this way, the second paper sensor 635 of the second edge sensor 63 measures the side edge position of the paper before skew correction at a plurality of locations in the transport direction according to the control of the pre-correction edge position measurement unit 61. By using the side edge positions measured at a plurality of locations for estimation by the position estimation unit 62, highly accurate position estimation values reflecting the state of skew are estimated.

  FIG. 9 is a diagram for explaining the calculation of the side edge position at the leading edge portion of the paper based on the side edge position of the paper measured at a plurality of positions by the position estimation unit shown in FIG.

  FIG. 9 shows a state U1 in which the sheet is conveyed toward the registration roll 21 (see FIG. 7), a state U2 after skew correction by the registration roll 21, and a state U3 in which an image is formed. The side edge positions L1 and L2 measured by the second paper sensor 635 in the state U1 before skew correction are shown. Here, in the two side edge positions L1 and L2, the lengths from the leading edge of the sheet in the state U1 in the sheet conveyance direction are measured at positions T1 and T2, respectively. Of the side edges of the paper in the state U1, the side edge position E at the leading edge of the paper that strikes the registration roll 21 is obtained by the following equation (1).

  E = L1 + (L2-L1) × T1 / (T2-T1) (1)

  When the sheet in the state U1 is abutted against the registration roll 21, the sheet rotates when viewed from above the image forming apparatus 1, the skew is corrected, and the state indicated by U2 is obtained. However, at this time, since the sheet rotates around a position different from the abutted leading edge, the side edge position L of the sheet in the state U2 in which the skew is corrected is the side edge position at the leading edge of the side edge in the state U1. Different from E. Here, the side edge position of the paper in the state U2 after the skew correction can be estimated by calculating the following equation (2).

L0 = E−d = E− (L1−L2) × K
= L1 + (L2-L1) * T1 / (T2-T1)-(L1-L2) * K (2)

  The side edge position estimated by the above equation (2) becomes the position estimated value L0.

  Here, K is the side edge position E at the front end of the paper calculated from the measurement results L1 and L2 of the paper in the state U1 before skew correction, which is calculated by the second edge sensor 63, for the paper that has been conveyed last time. The correlation parameter represents the degree of correlation with the position measurement value L obtained by measuring the side edge position of the sheet in the state U2 in the first sheet sensor 225 of the first edge sensor.

  The parameter calculation unit 64 shown in FIG. 6 uses the measurement results L1 and L2 of the sheet in the state U1 before skew correction in the second sheet sensor 635 and the first sheet sensor 225 in the state U2 of the sheet after skew correction. The correlation parameter K is calculated on the basis of the position measurement value L that is the side edge position. Specifically, a correlation parameter K is calculated that matches the position estimation value L0 calculated by the above equation (2) from the measurement results L1 and L2 before skew correction with the position measurement value L after skew correction. The correlation parameter K is specifically obtained by the following equation (3), which is a modification of the above equation (2).

K = (L− (L1 + (L2−L1) × T1 / (T2−T1))) / (L1−L2)
(3)

  The parameter calculation unit 64 stores the calculated correlation parameter K in the parameter storage unit 65. In this embodiment, the correlation parameter K is calculated every time a sheet is conveyed, and the correlation parameter K in the parameter storage unit 65 is updated each time a sheet is conveyed.

  The position estimation unit 62 illustrated in FIG. 6 stores the measurement results L1 and L2 by the second sheet sensor 635 in the state U1 before skew correction, and parameter storage for sheets conveyed after the sheet for which the correlation parameter K is calculated. Based on the correlation parameter K stored in the unit 65, the position estimated value L0 in the state U2 after skew adjustment is calculated by the above equation (2). Thereby, the side edge position of the sheet at the measurement position of the first sheet sensor 225 is estimated.

  Here, returning to FIG. 7, the first sheet P1 and the second sheet P2 conveyed after the first sheet P1 will be described. The skew of the first sheet P1 has already been corrected by being abutted against the registration roll 21 at the time shown in FIG. Before the first paper P 1 is abutted against the registration roll 21, the side edge positions L 1 and L 2 are measured by the second paper sensor 635, and then, after the first paper sensor 225 has passed the registration roll 21. The side edge position L of the paper is measured. Accordingly, the parameter calculation unit 64 calculates the correlation parameter K for the first sheet P1 and stores the correlation parameter K in the parameter storage unit 65.

  Thereafter, as shown in FIG. 7, when the second sheet P2 conveyed toward the registration roll next to the first sheet P1 passes the sheet sensor 68, the side edge of the second sheet P2 is reached. The positions L1 and L2 are measured by the second paper sensor 635. The position estimation unit 62 estimates the position estimation value L0 based on the measurement results L1 and L2 and the correlation parameter K stored in the parameter storage unit 65. Thereafter, the second paper P2 is abutted against the registration roll 21 as indicated by P2 'to correct the skew, and is sent to the transfer unit 15 by the registration roll 21. At this time, an electrostatic latent image corresponding to the second sheet P2 ′ is formed on the photosensitive drum 12, but the image position adjusting unit 34 is formed on the second sheet P2 ′. The image forming position M in the width direction of the image is adjusted based on the position estimated value L0 estimated by the position estimating unit 62.

  Further, after that, when the side edge position L is measured by the first sheet sensor 225 for the second sheet P2 ′, the parameter calculation unit 64 now has the side edge positions L1, L2 of the second sheet P2 ′. Based on the measurement result of L2 and the position measurement value of the side edge position L, the correlation parameter K for the second sheet P1 is calculated and stored in the parameter storage unit 65.

  FIG. 10 is a diagram for explaining the flow of position information for each sheet of the image forming apparatus shown in FIG.

  As shown in FIG. 10, the correlation parameter K for the first paper P1 calculated from the side edge positions L1, L2 of the first paper P1 and the side edge position L of the first paper P1 is calculated. From the correlation parameter K for the first sheet P1 and the side edge positions L1, L2 of the second sheet P2, the position estimated value L0 of the side edge position for the second sheet P2 is estimated. On the other hand, the correlation parameter K for the second paper P2 calculated from the side edge positions L1, L2 of the second paper P2 and the side edge position L of the second paper P2 is calculated, and the second paper P2 is calculated. From the correlation parameter K for P2 and the subsequent side edge positions L1, L2 of the third sheet, the position estimated value L0 of the side edge position for the third sheet P2 is estimated. Thereafter, the correlation parameter K is calculated based on the measured values of the sequentially conveyed sheets, and the position estimation value for the next sheet is further estimated based on the correlation parameter K.

  According to the image forming apparatus 2 of the present embodiment, the sheet conveyed after the next time is estimated from the measurement results L1 and L2 of the position before skew correction and the correlation parameter K adjusted based on the actual measurement. Since the image forming position M is adjusted based on the estimated position L0 after skew correction, the change in the position in the width direction for each of the sheets P1 and P2 that are continuously conveyed is reflected in the adjustment. The displacement of the position of the image formed is suppressed.

  In the present embodiment, an example in which measurement is performed at two positions as an example of measuring the side edge position of a sheet at a plurality of positions has been described. However, the present invention is not limited to this, and measurement is performed at, for example, three or more positions. It may be done.

  Further, the measurement location of the side edge position may be one. However, by measuring the positions at a plurality of locations and using them for estimation, a highly accurate position estimation value that reflects the state of the skew before skew correction is estimated. Therefore, the displacement of the position of the image formed on the paper is further suppressed.

  Further, in the present embodiment, each time a sheet is conveyed, the stored content is updated by storing the correlation parameter K based on the measurement result of the side edge position in the parameter storage unit. Is not limited to this. For example, after the parameters are stored based on the measurement results for the first sheet, a plurality of sheets conveyed following the first sheet may be reused without updating the parameters. .

  In the present embodiment, as a method for calculating a parameter for obtaining a position estimated value that matches the position measured value, the position estimated value calculated by the position estimating unit 62 from the measurement results L1 and L2 before skew correction. Although the correlation parameter K for matching L0 with the position measurement value L after skew correction is calculated, the present invention is not limited to this. For example, the parameter calculation may use feedback control that increases or decreases the parameter based on the difference between the position estimation value actually estimated by the position estimation unit and the position measurement value.

  In the image forming apparatus of the above-described embodiment, the first paper sensor 225 measures the position in the width direction of the paper conveyed toward the image forming mechanism 10 once. Next, in the first embodiment, a modified example in which the measurement by the first sheet sensor 225 is performed a plurality of times will be described.

  FIG. 11 is a flowchart for explaining processing of the post-correction edge position measurement unit and the image position adjustment unit in the modification of the first embodiment.

  In this modification, the corrected edge position measurement unit 35 waits until the sheet passes the registration roll 21 (step S11), and the first sheet sensor 225 sets the sheet side edge positions s1 and s2 at two locations. Measurement is performed (step S12). Next, the average value L is calculated from the side edge positions s1 and s2 at two locations (step S13). The image position adjustment unit 34 calculates the image writing position M of the next sheet based on the average value L (step S14).

  The paper may be slightly skewed even after the skew is corrected by the registration roll 21. By measuring positions at a plurality of positions on the sheet by the first sheet sensor 225, the side edge position can be grasped more accurately.

  Subsequently, another modification example of the modification example of the first embodiment described above will be described.

  FIG. 12 is a flowchart for explaining processing of the corrected edge position measurement unit and the image position adjustment unit in another modification of the first embodiment.

  In this modification, the corrected edge position measurement unit 35 waits until the sheet passes the registration roll 21 (step S21), and the first sheet sensor 225 sets the side edge positions s1 and s2 of the sheet at two locations. Measurement is performed (step S22). Next, a difference K is calculated from the side edge positions s1 and s2 at two locations (step S23), and a paper skew amount S considering the paper size is calculated from the difference K (step S24). Next, it is determined whether or not the skew amount S exceeds the minimum value of the abnormal value range as a predetermined threshold (step S25), and when the skew amount S does not exceed the minimum value of the abnormal value range. The image position adjusting unit 34 calculates the image writing position M of the next sheet and repeats the process. On the other hand, when the skew amount S exceeds the minimum value of the abnormal value range, it is determined that the skew of the sheet is abnormal, and the operation of the image forming apparatus 1 is stopped.

  If the skew of the paper is too large, the image cannot be formed normally and may cause a paper jam, so it is necessary to stop the operation. According to this modification, the measurement is performed by the first edge sensor. It is possible to easily determine whether to stop the operation by using the difference in the position in the width direction at the plurality of locations.

  Note that the two modifications described above have been described as modifications of the first embodiment, but these modifications can also be applied to the image forming apparatus of the second embodiment.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the external appearance of the 1st edge sensor shown in FIG. FIG. 2 is a functional block diagram of the image forming apparatus 1 shown in FIG. 1. FIG. 2 is a diagram illustrating a state in which an image is formed on a sheet by the image forming apparatus illustrated in FIG. 1. It is a schematic block diagram of the image forming apparatus of 2nd Embodiment of this invention. FIG. 6 is a functional block diagram of the image forming apparatus shown in FIG. 5. FIG. 6 is a diagram illustrating a state in which an image is formed on a sheet by the image forming apparatus illustrated in FIG. 5. It is a figure explaining the measurement of the side edge position of the paper by the 2nd edge sensor. FIG. 7 is a diagram for explaining calculation of a side edge position at a front end portion of a sheet based on a side edge position of the sheet measured at a plurality of positions by the position estimation unit illustrated in FIG. It is a figure explaining the flow of the positional information for every paper of the image forming apparatus shown in FIG. It is a flowchart explaining the process of the post-correction edge position measurement part and image position adjustment part in the modification of 1st Embodiment. It is a flowchart explaining the process of the post-correction edge position measurement part and image position adjustment part in another modification of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Image forming apparatus 10 Image forming mechanism 11 Scanner 12 Photosensitive drum 15 Transfer unit 20 Paper transport mechanism 21 Registration roll 22 First edge sensor 221 Arm 222 Motor 225 First paper sensor (first sensor)
24, 25 Transport roll 30, 60 Control unit 31 Scan control unit 32 Mechanism control unit 33 Transport control unit 34 Image position adjustment unit 35 Corrected edge position measurement unit 36 Position information storage unit 65 Parameter storage unit 61 Pre-correction edge position measurement unit 62 Position Estimation Unit 63 Second Edge Sensor 632 Motor 635 Second Paper Sensor (Second Sensor)
64 Parameter calculation unit 66 Image position adjustment unit

Claims (6)

  An image forming unit that forms an image on the conveyed paper and that can freely adjust the image forming position in the width direction perpendicular to the paper transport direction, and transports the paper on a paper transport path that passes through the image forming unit. A paper transport unit,
  The paper transport unit is
  A pair of rolls arranged in contact with each other to form a nip area disposed upstream of the image forming unit from the image forming unit, and the sheet is abutted against the nip area to correct the skew of the sheet. And a registration roll for feeding the paper to the image forming unit in accordance with the timing of image formation in the image forming unit,
  A first sensor that is provided between the registration roll and the image forming unit and that measures the position in the width direction of the first sheet that has been transported this time toward the image forming unit;
  A second sensor that is disposed upstream of the registration roll in the transport direction and that measures the position in the width direction of the first paper transported this time toward the registration roll;
  The position of the first sheet in the width direction at the measurement position of the first sensor is estimated based on the measurement result of the second sensor of the first sheet conveyed this time and a predetermined parameter. A position estimation unit for obtaining a position estimated value;
  A parameter calculation unit that calculates a parameter for obtaining a position estimated value that matches a position measurement value obtained by measuring the position of the first sheet in the width direction by the first sensor;
  A parameter storage unit for storing parameters calculated by the parameter calculation unit,
  When the position estimation unit obtains a position estimation value for the second sheet conveyed from the next time onward, it is stored in the parameter storage unit and the measurement result of the second sheet by the second sensor. A position estimation value for the second sheet is obtained by estimating the position in the width direction of the second sheet based on
  The image forming unit adjusts the image forming position in the width direction of the image formed on the second sheet based on the position estimation value of the second sheet obtained by the signal estimating unit. An image forming apparatus, comprising:   The second sensor measures the position in the width direction of the paper being transported at a plurality of locations in the transport direction of the paper;
  The position estimation unit determines the first sheet at the measurement position of the first sensor based on the measurement result of the second sensor at a plurality of locations on the first sheet and a predetermined parameter. In estimating the position in the width direction to obtain a position estimated value, and obtaining the position estimated value for the second sheet conveyed from the next time onward, the second at a plurality of positions on the second sheet. The position in the width direction of the second sheet is estimated based on the measurement result of the sensor and the parameters stored in the parameter storage unit, and the position estimated value for the second sheet is obtained. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   The first sensor and the second sensor are respectively a first paper sensor and a second paper sensor that detect the presence or absence of paper,
  2. The image forming apparatus includes a first moving unit and a second moving unit that move the first sheet sensor and the second sheet sensor in the width direction. The image forming apparatus described.   If the first sheet is the first sheet conveyed by the sheet conveying unit after the type of the sheet conveyed by the sheet conveying unit is changed, the position estimating unit The first sheet at the measurement position of the first sensor based on a measurement result of the first sheet by the second sensor and an initial value predetermined according to the type of the first sheet. The image forming apparatus according to claim 1, wherein the position estimation value is obtained by estimating the position in the width direction.   2. The first sensor according to claim 1, wherein the first sensor measures the position in the width direction of the sheet conveyed toward the image forming unit at a plurality of locations in the conveyance direction of the sheet. Image forming apparatus.   In the image forming unit and the sheet conveying unit, the difference in the position in the width direction at a plurality of positions of the sheet conveyed toward the image forming unit measured by the first sensor exceeds a predetermined threshold. 6. The image forming apparatus according to claim 5, wherein in the case, the operation is stopped.

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