JP4227367B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, after a toner image formed on an image carrier such as a photosensitive drum is transferred to a sheet, the toner image is fixed on the sheet by a fixing unit such as a thermal fixing unit or a pressure fixing unit. I have an image.
[0003]
Conventionally, in such an image forming apparatus, there is an image forming apparatus that repeats a series of image forming operations from image transfer to fixing on the same sheet to obtain a multiple transfer image and a double-sided image.
[0004]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, when the image is fixed on the sheet by the fixing unit, the sheet expands and contracts due to the influence of heat and pressure. If image formation is repeated repeatedly, the image magnification will be different between the previous image whose size has changed with the expansion and contraction of the sheet and the next image to be transferred next, resulting in a relative image shift and the quality of the output image. Will fall.
[0005]
Therefore, the present invention makes it possible to match the relative image positions of the previous image and the next image with high accuracy without being affected by the expansion and contraction of the sheet due to fixing even when image formation is performed a plurality of times on the same sheet. It is an object of the present invention to provide an image forming apparatus that can be used.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image forming unit that forms an image on an image carrier in accordance with an image forming signal, and an image carrier by the image forming unit. A transfer means for transferring the image formed on the sheet to the sheet; a fixing means for fixing the image transferred by the transfer means to the sheet; and a sheet length in the sheet conveyance direction and a sheet width in the direction perpendicular to the conveyance direction. A sheet size measuring unit that measures before and after fixing of a transfer image by the fixing unit, and a re-conveying unit that inverts the front and rear ends and also reverses the front and back after the fixing to the transfer unit, I have a,
Based on the measurement of the sheet size by the sheet size measuring unit before and after fixing the sheet on which the previous image is transferred when the sheet is re-conveyed by the re-conveying unit and the image is transferred to the same sheet a plurality of times. An image forming apparatus for changing the image magnification of the next image to be transferred next and the image position with respect to the sheet to match the previous image with the next image,
An error dimension between the normal dimension of the sheet and the dimension of the sheet before fixing the previous image measured by the sheet size measuring unit is calculated, and before fixing and fixing of the previous image measured by the sheet size measuring unit By calculating the ratio of the dimensions of the subsequent sheet and changing the image position by a value calculated by multiplying the error dimension and the ratio, the image leading edge position of the next image and the image trailing edge position of the previous image are obtained. It is characterized by matching on the front and back of the sheet .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. 1 is a cross-sectional view of an image forming apparatus according to the present embodiment, FIGS. 2 to 3 are explanatory views of a sheet length detection device, FIGS. 4 to 6 are explanatory views of a sheet width detection sensor, and FIGS. It is explanatory drawing of the image position transcribe | transferred on a sheet | seat.
[0008]
As shown in FIG. 1, the image forming apparatus is a digital copying machine that has a printer function and a copying function and forms an image based on image information transmitted from an external device such as a controller or an image reading unit 100.
[0009]
The digital copying machine includes an image reading unit 100, an image processing unit (not shown) that generates an image forming signal based on image information, an image forming unit 101 that is an image forming unit, sheet cassettes C1 and C2, and a sheet. A feeding unit 102 that feeds the sheet P from the cassettes C1 and C2, a transfer conveyance unit 103 that conveys the sheet P to the transfer point A, a fixing device 104 as fixing means, and a fixing device 104 that transfers the sheet P after transfer. A fixing conveyance unit 105 that conveys the sheet to the outside, a discharge processing unit 106 that switches the sheet path during both-side discharge and double-sided / multi-transfer, and a double-side / side-side reverse that reverses the sheet path for double-sided or multiple transfer. A multi-processing unit 107 and a double-sided / multi-conveying unit 108 that conveys the sheet P to the transfer / conveying unit 103 again when double-sided or multiple images are formed are provided.
[0010]
The image forming unit 101 emits light from the laser exposure device 109 in response to an image forming signal generated by an image processing unit based on image information transmitted from an external device (not shown) such as a controller or the image reading unit 100. The developing device 2 develops an electrostatic latent image obtained by forming an image of the laser beam L on the photosensitive drum 1 to form a toner image. A primary charger 3 and a cleaning device 4 are arranged around the photosensitive drum 1. Further, at the transfer point A, a transfer roller 5 serving as a transfer unit is disposed to face the photosensitive drum 1, and a sheet conveyed from the registration roller pair 11 of the transfer conveyance unit 103 in synchronization with the toner image on the photosensitive drum 1. A toner image is transferred onto P. The sheet P on which the toner image is transferred is conveyed to the fixing device 104 by the fixing conveyance unit 105.
[0011]
The sheet P on which the image is fixed after passing through the fixing device 104 passes through the discharge processing unit 106 and is discharged to the outside of the apparatus or sent to the double-side / multi-processing unit 107 according to the operation sequence. During double-sided or multiple transfer, the sheet P is route-changed by the first route switching device 12 of the discharge processing unit 106 and conveyed to the double-sided / multi-processing unit 107. The sheet P conveyed to the duplex / multiple processing unit 107 is further sent by the second path switching device 13 to the duplex / multiple conveyance unit 108 at the time of multiple transfer and to the reversing roller 14 at the time of double-sided transfer. The front end and the rear end are reversed and the front and back are reversed, and then conveyed to the double-sided / multiple conveying unit 108. Then, the sheet P is sent again from the duplex / multi-conveyance unit 108 to the transfer conveyance unit 103, and the next image transfer is performed.
[0012]
The transfer conveyance unit 103 includes a skew correction device 111, a sheet length detection device 110 and a sheet width detection sensor 35 as sheet size measurement means, and performs skew correction and sheet size measurement of the sheet P before transfer. ing. In addition, the sheet size is measured before the image forming signal is generated in the image processing unit. When image formation is repeatedly performed on both sides or in multiples, the next image with respect to the previous image is determined according to the sheet size measurement result. The image processing unit generates an image forming signal in which the image magnification and the image forming position are changed.
[0013]
The sheet length detection device 110 includes a conveyance roller pair 21 that is a sheet restraining unit that conveys the sheet P at a constant speed, a sheet leading edge passage sensor 22 disposed on the downstream side of the conveyance roller pair 21, and a conveyance roller pair 21. A sheet rear end passage sensor 23 disposed on the upstream side is provided, the passage timing of the front end of the sheet P conveyed by the conveying roller pair 21 is detected by the sheet front end passage sensor 22, and then the passage timing of the rear end of the sheet P is detected. It is detected by the rear end passage sensor 23.
[0014]
Here, as shown in FIG. 2A, the conveyance roller pair 21 has a plurality of conveyance roller portions 21a that come into contact with the sheet P, and a small-diameter portion 21b that is provided coaxially with the conveyance roller portion 21a. The sheet leading edge passage sensor 22 and the sheet trailing edge passage sensor 23 are provided close to the upstream and downstream spaces of the small diameter portion 21b sandwiched between the two conveying roller portions 21a. Therefore, as shown in FIGS. 2B and 2C, the sheet leading edge passing sensor 22 and the sheet trailing edge passing sensor 23 are constrained by the conveying roller pair 21, and the leading edge of the sheet P is located near the conveying nip where there is little flapping. The passage of the rear end can be detected.
[0015]
At this time, the conveying speed of the sheet P conveyed to the conveying roller pair 21 is V, the interval between the sheet leading edge passing sensor 22 and the sheet trailing edge passing sensor 23 is L0, and the time difference between the passing timings of the leading and trailing edges of the sheet P is expressed as follows. When ΔT, the sheet length L in the conveyance direction of the sheet P is calculated by the following formula: L = VΔT + L0 (1)
[0016]
In the image forming apparatus of the present embodiment, a pair of conveying rollers and two sensors are used as the sheet length detection device. However, as shown in FIG. 3, two pairs of conveying rollers 41 and 42 are used. Further, the sheet length can be calculated from the time difference between the sheet leading edge and the trailing edge by detecting the leading edge and the trailing edge of the sheet by one sensor 43 disposed therebetween. In this case, the sheet length L ′ is calculated by the following equation using the time difference between the passage timings of the leading and trailing edges of the sheet as ΔT ′: L ′ = VΔT ′ (1 ′)
[0017]
On the other hand, as shown in FIG. 4, the skew correction device 111 includes an abutting member 31 arranged in parallel to the sheet conveying direction, and oblique running rollers 32, 33, and 34 that are abutting means. The rollers 32, 33, and 34 correct the skew of the sheet P by conveying the sheet P while abutting the left end of the sheet P in the abutting member 31 direction. Further, a sheet width detection sensor 35 is provided on the right end side of the sheet P conveyed while being abutted against the abutting member 31, and detects the position of the right end of the sheet P where the left end is abutted against the abutting member 31. . Thus, the distance between the abutting member 31 and the right end of the sheet P can be measured as the width W of the sheet P perpendicular to the conveying direction.
[0018]
A non-contact type sensor such as a CCD sensor is widely used as a sensor for detecting the position at the sheet end, such as the sheet width detection sensor 35, but the position of the sheet end is detected by a non-contact type sensor. In such a case, there is a concern that the detection accuracy may be lowered due to undulation or fluttering of the sheet being conveyed. Therefore, as shown in FIG. 5, by providing a pair of conveying rollers 45 and 46 for restraining the sheet end portions on the upstream side and the downstream side of the sheet width detection sensor 35, as shown in FIG. Since fluttering can be suppressed and the distance between the sheet width detection sensor 35 and the sheet P can be kept constant, the detection accuracy can be improved. Further, the conveyance roller pair 45, 46 has a sheet conveyance force, and the sheet conveyance speed by the conveyance roller pair 46 on the downstream side in the conveyance direction of the sheet width detection sensor 35 is set to the conveyance roller pair on the upstream side in the conveyance direction of the sheet width detection sensor 35. By making the speed faster than 45, it is possible to prevent the sheet from sagging in the region sandwiched between the pair of conveying rollers 45 and 46. Further, when the right end of the sheet P is detected by the sheet width detection sensor 35, the detection accuracy can be further improved by temporarily stopping the conveyance of the sheet P.
[0019]
Further, by providing a moving means for moving the sheet width detection sensor 35 in the sheet width direction, it is possible to cope with a plurality of sheet widths.
[0020]
In the present embodiment, the conveyance roller pair 21 and the conveyance roller pairs 45 and 46 are used as the sheet restraining means for constraining the sheet P at the time of detection, but a cylindrical member or a flexible member that contacts the sheet without having the sheet conveyance force. Any holding member can be used as long as it can hold the sheet to be conveyed, such as an adhesive sheet, to suppress fluttering of the sheet, and this sheet restraining means enables highly accurate detection.
[0021]
Here, the conveyance direction image length LG1 (=) which matches the normal dimension (length L0, width W0) of the standard size of the sheet P to the sheet P having the sheet length L1 in the conveyance direction and the sheet width W1 perpendicular to the conveyance direction. FIG. 7 shows the positional relationship between the sheet P and the image G1 when the image G1 having an image width WG1 (= W0) perpendicular to the conveying direction is transferred. At this time, the sheet P has an error dimension of EL1 in the length direction and EW1 in the width direction with respect to the normal dimensions (length L0, width W0), and the length LG1 and the width WG1 of the image G1 are Including left and right margin dimensions. In this embodiment, the image is positioned with reference to the leading end T in the conveyance direction of the sheet P and the left end L that is abutted against the abutting member 31 for skew feeding correction.
[0022]
FIG. 8 shows the position and dimensional relationship between the sheet P and the image G1 that are again conveyed to the transfer conveyance unit 103 after passing through the fixing device 104 when multiple image formation is performed. The size of the sheet P changes to the length L2 and the width W2 due to expansion and contraction when passing through the fixing device 104, and the size of the image G1 also changes to the length LG2 and width WG2 as the sheet P expands and contracts. That is, LG2 and WG2 can be expressed as follows: LG2 = L2 / L1 · LG1 (2)
WG2 = W2 / W1 / WG1 (3)
[0023]
In this embodiment, when the image processing unit generates an image formation signal for the next image, the sizes L1 and W1 of the sheet P before the image formation measured by the sheet length detection device 110 and the sheet width detection sensor 35 are used. Then, the image size is changed according to the expressions (2) and (3) from the sizes L2 and W2 of the sheet P before the next image formation, and the image is positioned with reference to the leading edge T and the left edge L of the same sheet P as the previous image. By doing so, the previous image and the next image are made to coincide.
[0024]
On the other hand, FIG. 9 shows the position and dimensional relationship between the sheet P and the image G1 that are reversed from the front and back after passing through the fixing device 104 and conveyed again to the transfer conveyance unit 103 when performing double-sided image formation. The size of the sheet P changes to a length L2 and a width W2 due to expansion and contraction when passing through the fixing device 104, as in the case of multiple image formation, and the size of the image G1 also changes to the length LG2, as the sheet P expands and contracts. The width changes to WG2. Furthermore, the positions of the front end T and the rear end E of the sheet P are switched by the front / back reversal, and the image G1 moves to the back side.
[0025]
Here, as a result of switching the positions of the leading edge T and the trailing edge E of the sheet P, the trailing edge E of the sheet P at the time of forming the previous image becomes a positioning reference in the conveyance direction of the next image. Further, a gap between the positioning reference E in the conveyance direction of the next image and the image rear end EG of the front-side front image G1 is caused by a dimensional error EL1 in the length direction of the sheet P and can be expressed as the following equation. EL2 is generated EL2 = L2 / L1 · EL1
= L2 / L1 · (L1-L0) (4)
[0026]
Therefore, at the time of double-sided image formation, when the image forming signal for the next image is generated by the image processing unit, in addition to the image size change according to the equations (2) and (3), it is calculated by the equation (4). The position of the image is moved in accordance with EL2, so that the leading edge position of the next image matches the trailing edge EG of the previous image.
[0027]
In the present embodiment, the size and position of the next image are changed using image processing. However, the image clock frequency of the laser beam is changed, the rotation speed of the polygon mirror is changed, and the laser optical system is changed. The image size and position can be changed by moving the lens and the reflecting mirror.
[0028]
As described above, the image forming signal of the next image in which the image size / position is changed based on the sheet size before and after fixing the previous image measured by the sheet size measuring unit at the time of forming the multiple / double-sided image. By generating in the forming unit, it is possible to prevent relative image shift of the multiplexed / double-sided image.
[0029]
【The invention's effect】
As described above, by changing the image magnification of the next image and the position relative to the sheet based on the measurement result of the sheet size before and after fixing by the sheet size measuring unit, the dimensional error, variation, and dimensional change of the sheet Therefore, it is possible to prevent image misalignment during multiple / double-sided image formation and to obtain a high-quality output image.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a digital copying machine according to an embodiment.
FIG. 2 is an explanatory diagram of a sheet length detection device.
FIG. 3 is an explanatory diagram of a sheet length detection device.
FIG. 4 is an explanatory diagram of a sheet width detection sensor.
FIG. 5 is an explanatory diagram of a sheet width detection sensor.
FIG. 6 is an explanatory diagram of a sheet width detection sensor.
FIG. 7 is an explanatory diagram of image positions transferred on a sheet.
FIG. 8 is an explanatory diagram of image positions transferred on a sheet.
FIG. 9 is an explanatory diagram of image positions transferred on a sheet.
[Explanation of symbols]
A: Transfer points C1, C2 ... Sheet cassette L ... Laser beam P ... Sheet 1 ... Photosensitive drum 2 ... Developer 3 ... Primary charger 4 ... Cleaning device 5 ... Transfer roller
11… Registration roller pair
12 ... 1st course switching device
13 ... Second route switching device
14… Reverse roller
21… Conveying roller pair
21a ... Conveyance roller section
21b ... Small diameter part
22, 23… Seat rear end passage sensor
31… Abutting member
32 to 34 ... Rolling roller
35… Sheet width detection sensor
41, 42… Conveying roller pair
43… Sensor
45, 46… Conveying roller pair
100 ... Image reading unit
101… Image creation department
102… Feeding department
103 Transfer transfer section
104… Fixing device
105… Fixing transport section
106… Discharge processing section
107… Double-sided / multi-processing part
108… Double-sided / Multi-transport part
109 ... Laser exposure apparatus
110 ... Sheet length detection device
111 ... Skew correction device

Claims (9)

An image forming unit that forms an image on the image carrier in response to an image forming signal, a transfer unit that transfers an image formed on the image carrier by the image forming unit to a sheet, and a transfer unit that transfers the image. Fixing means for fixing the image on the sheet, sheet size measuring means for measuring the sheet length in the conveyance direction of the sheet and the sheet width in the direction perpendicular to the conveyance direction before and after fixing the transferred image by the fixing means, the sheet obtained by inverting the front and back as well as reverses the leading and trailing ends after fixing have a, a re-conveying means for conveying back to said transfer means,
Based on the measurement of the sheet size by the sheet size measuring unit before and after fixing the sheet on which the previous image is transferred when the sheet is re-conveyed by the re-conveying unit and the image is transferred to the same sheet a plurality of times. An image forming apparatus for changing the image magnification of the next image to be transferred next and the image position with respect to the sheet to match the previous image with the next image,
An error dimension between the normal dimension of the sheet and the dimension of the sheet before fixing the previous image measured by the sheet size measuring unit is calculated, and before fixing and fixing of the previous image measured by the sheet size measuring unit By calculating the ratio of the dimensions of the subsequent sheet and changing the image position by a value calculated by multiplying the error dimension and the ratio, the image leading edge position of the next image and the image trailing edge position of the previous image are obtained. An image forming apparatus characterized by matching on the front and back of a sheet .   The image forming apparatus according to claim 1, wherein the sheet size measuring unit includes a sheet restraining unit that restricts the movement of the sheet in a direction different from the sheet conveyance direction when the size of the sheet is measured.   The sheet size measuring unit includes a sheet passage sensor that detects a front end and a rear end of a conveyed sheet, and the sheet restraining unit is disposed on the left and right of the sheet passage sensor and includes a holding member that holds the conveyed sheet. The image forming apparatus according to claim 2, further comprising:   The nipping member is a conveying roller pair having a roller portion and a small diameter portion that supports the roller portion, and the sheet passing sensor is disposed in proximity to the small diameter portion of the conveying roller pair. The image forming apparatus according to 3.   An abutting member disposed in parallel to the sheet conveying direction; and an abutting unit that abuts one side of a sheet edge parallel to the conveying direction to the abutting member, and the sheet size measuring unit includes the abutting unit A sheet width detection sensor that detects an edge position on the other side of the sheet edge that is abutted against the abutting member by the means, and the sheet restraining means includes an upstream side and a downstream side in the sheet conveyance direction of the sheet width detection sensor. The image forming apparatus according to claim 2, further comprising a clamping member that is disposed on the sheet and clamps the sheet to be conveyed.   The image forming apparatus according to claim 5, wherein the clamping member is a pair of conveyance rollers disposed in the vicinity of the upstream side and the downstream side in the sheet conveyance direction of the sheet width detection sensor.   The sheet conveyance speed by the conveyance roller pair provided on the downstream side in the sheet conveyance direction of the sheet width detection sensor is made faster than the sheet conveyance speed by the conveyance roller pair provided on the upstream side in the sheet conveyance direction of the sheet width detection sensor. The image forming apparatus according to claim 6.   The image forming apparatus according to claim 5, wherein the conveyance of the sheet is stopped when the sheet edge position is detected by the sheet width detection sensor.   9. The image forming apparatus according to claim 1, further comprising a moving unit that moves the sheet size measuring unit to a position corresponding to the size of the sheet to be conveyed.

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