JP5339894B2 - Image forming apparatus - Google Patents

Description

The present invention is a copying machine provided with a sheet conveying equipment for detecting the leading edge of the sheet, the printer, an image forming apparatus such as a facsimile.

  Conventionally, there is provided a sheet conveyance device called a cut sheet, in which a sheet previously cut into a standard size is stored in a sheet storage unit, and sheets fed from the sheet storage unit are continuously conveyed to an image forming unit. An image forming apparatus is known. Then, in order to improve the throughput (the number of sheets conveyed per unit time), the sheet is formed in the image forming unit in a state where the interval between the sheets is 0 or close to 0, or in a state where the sheets are partially overlapped. To form an image on a sheet.

  In this type of image forming apparatus, detection of the leading edge of the sheet becomes a problem. That is, when a sheet is conveyed in a state where the interval between the sheets is 0 or close to 0, or in a state where the sheets are overlapped, it is difficult to detect the leading edge of the sheet other than the leading sheet. And when performing various controls by detecting the leading edge of the sheet, for example, when synchronizing the leading edge of the sheet and the leading edge of the image formed by the image forming unit, if the leading edge of the sheet cannot be detected, Various problems occur such as it becomes difficult to form an image accurately.

  Therefore, a method has been proposed in which the leading edge of the succeeding sheet is separated from the trailing edge of the preceding sheet by a curved guide in the sheet conveyance path, and the leading edge of the separated succeeding sheet is detected by the leading edge detecting means (see Patent Document 1). ). The tip detection means includes a photo interrupter arranged outside the curved guide, and a sensor arm that protrudes into the curved guide and is rotatably supported. When the sheet conveyed in an overlapping manner is conveyed along the curved guide, the leading edge of the next succeeding sheet overlapping the preceding preceding sheet is separated from the preceding sheet. For this reason, the leading edge of the succeeding sheet away from the preceding sheet presses the sensor arm and the photo interrupter is turned on, so that the leading edge of the sheet can be detected.

JP 2000-198575 A

  However, in the detection method described above, since the sheet is bent and separated, the position of the leading edge of the sheet varies slightly depending on the amount of bending of the sheet. Further, since the position where the sheet leading edge comes into contact with the sensor arm also varies, there is a problem that the sheet leading edge detection accuracy is low.

The present invention is aimed at providing the images forming apparatus that can be improved tip detection accuracy of the sheet.

An image forming apparatus according to the present invention includes a sheet conveying device that continuously conveys sheets at intervals that cannot be detected by a leading edge detection unit, and an image forming unit that forms an image on a sheet conveyed by the sheet conveying device. in the image forming apparatus, the sheet transport device, and an offset portion which is offset in the offset direction of the succeeding sheet orthogonal to the sheet conveying direction trailing against the preceding preceding sheet and the subsequent sheet is transported, which is offset by the offset section A leading edge detector that detects the leading edge of the offset portion of the succeeding sheet , and the succeeding sheet detected by the leading edge detector is perpendicular to the sheet conveyance direction and opposite to the offset direction. A shift portion that shifts in the direction, and based on the detection result of the tip detection portion, Serial synchronizing the tip of an image to be formed by the image forming unit, it is characterized in.

  According to the present invention, when the sheets are conveyed in a state where the distance between the sheets is 0 or close to 0, or when the sheets are overlapped with each other, The tip can be detected with high accuracy.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of a printer that is an example of an image forming apparatus including a sheet conveying device according to a first embodiment of the present invention.

  In FIG. 1, reference numeral 1000 denotes a printer. The printer 1000 includes a printer main body 1001 and a scanner 2000 disposed on the upper surface of the printer main body 1001.

  Here, the scanner 2000 that reads a document includes a scanning optical system light source 201, a platen glass 202, and a document pressure plate 203 that opens and closes. An image reading unit 2001 including a lens 204, a light receiving element (photoelectric conversion element) 205, an image processing unit 206, a memory unit 208 for storing image processing signals processed by the image processing unit 206, and the like. I have.

  When reading the original, the original (not shown) placed on the platen glass 202 is read by irradiating light with the scanning optical system light source 201. Then, the read document image is processed by the image processing unit 206, converted into an electrically encoded electric signal 207, and transmitted to the laser scanner 111 as an image forming unit. Note that the image information processed and encoded by the image processing unit 206 may be temporarily stored in the memory unit 208 and transmitted to the laser scanner 111 as necessary by a signal from the controller 120.

  The printer main body 1001 includes an image forming unit 1003 that forms an image on the sheet S, a sheet conveying device 1004 that conveys the sheet S to the image forming unit 1003, a controller 120 that is a control unit for controlling the printer 1000, and the like. I have.

  The sheet conveying apparatus 1004 includes a sheet feeding apparatus 1002 that feeds the sheet S, a vertical path 108 that is arranged substantially vertically, and a sheet conveyance that is arranged substantially horizontally on the downstream side of the vertical path 108 in the sheet conveying direction. And a horizontal path 110 as a road. Further, the sheet conveying apparatus 1004 includes a vertical path roller pair 105 (105a, 105b) disposed in the vertical path 108 and a registration unit 1 disposed in the horizontal path 110. Here, the vertical path 108 includes a pair of guide plates 106 and 107. Further, the horizontal path 110 is constituted by a pair of guide plates 109a and 109b.

  A sheet feeding apparatus 1002 includes a separation unit including a cassette 100, a pickup roller 101, a feed roller 102, and a retard roller 103. The sheets S in the cassette 100 are separated and fed one by one by the action of the pickup roller 101 that moves up and down / rotates at a predetermined timing and the separation unit.

  The sheet S fed from the sheet feeding apparatus 1002 passes through the vertical path 108 by the vertical path roller pair 105, is then guided to the registration unit 1 disposed in the horizontal path 110, and is conveyed to the image forming unit 1003.

  The sheet feeding apparatus 1002 can continuously feed the sheets S one by one, and can continuously convey the sheets S one by one to the vertical path 108 and the horizontal path 110. By continuously conveying the sheet S in this way, the throughput is improved.

  The registration unit 1 includes an assist roller pair 10 that is disposed in the horizontal path 110 and is a pair of conveyance rollers as an offset unit, and can move in a direction orthogonal to the sheet conveyance direction while sandwiching the sheet S. In addition, the registration unit 1 includes a skew correction roller pair 21 and 22 that are disposed on the downstream side of the assist roller pair 10 in the sheet conveyance direction in the horizontal path 110. Further, the registration unit 1 includes a registration roller pair 30 as a shift unit disposed on the downstream side in the sheet conveyance direction of the skew correction roller pair 21 and 22 in the horizontal path 110.

  The image forming unit 1003 is an electrophotographic system, and includes a photosensitive drum 112 as an image carrier, a laser scanner 111 as an image writing unit, a developing device 114, a transfer charger 115, a separation charger 116, and the like.

  When forming an image, first, the laser beam from the laser scanner 111 is turned back by the mirror 113 and irradiated to the exposure position (laser beam irradiation position) 112a on the photosensitive drum rotating in the clockwise direction. A latent image is formed on the photosensitive drum. Further, the latent image formed on the photosensitive drum in this way is thereafter visualized as a toner image by the developing device 114.

Next, the toner image on the photosensitive drum thus visualized is transferred to the sheet S by the transfer charger 115 in the transfer unit 112b. The distance to the transfer section 112b from the exposure position 112a on the photosensitive drum 112 has a _{l 0.}

  Further, the sheet S on which the toner image is transferred in this manner is electrostatically separated from the photosensitive drum 112 by the separation charger 116 and then conveyed to the fixing device 118 by the conveyance belt 117 to fix the toner image. Thereafter, the sheet is discharged by the discharge roller 119.

  In FIG. 1, reference numeral 131 denotes a registration sensor as a leading edge detection unit provided on the downstream side in the sheet conveyance direction of the registration roller pair 30. The registration sensor 131 detects the leading edge of the sheet S that has passed through the registration roller pair 30. Detect. When the registration sensor 131 detects the leading edge of the sheet S that has passed through the registration roller pair 30, the controller 120 sends a sheet leading edge signal (image destination signal) to the laser scanner 111 after a predetermined time based on this detection signal. Thereby, irradiation of the laser beam by the laser scanner 111 is started.

  In this embodiment, the printer main body 1001 and the scanner 2000 are separate, but the printer main body 1001 and the scanner 2000 may be integrated. In addition, the printer main body 1001 functions as a copying machine when a processing signal of the scanner 2000 is input to the laser scanner 111, and functions as a facsimile when a facsimile transmission signal is input. Furthermore, if an output signal of a personal computer is input, it functions as a printer.

  Conversely, if the processing signal of the image processing unit 206 of the scanner 2000 is transmitted to another facsimile, it functions as a facsimile. If the scanner 2000 is equipped with an automatic document feeder 250 as shown by a two-dot chain line in place of the original pressure plate 203, the original can be automatically read.

  Next, the resist unit 1 will be described. FIG. 2 is a diagram for explaining the configuration of the registration unit 1 provided in the horizontal path 110, and FIG. 3 is a control block diagram of the registration unit 1.

  The horizontal path 110 serving as a sheet conveyance path is disposed on the upstream side in the sheet conveyance direction of the image forming unit 1003 (see FIG. 1). The roller pairs 10, 21, 22, and 30 arranged in the horizontal path 110 are A frame (not shown) is rotatably supported. That is, the registration unit 1 having the roller pairs 10, 21, 22, and 30 is disposed upstream of the image forming unit 1003 in the sheet conveyance direction.

  Here, when the registration sensor 131 detects the leading edge of the sheet, if the interval between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is short or the sheets overlap each other, The tip may not be detected. That is, when the sheets are continuously conveyed, the sheet sensor cannot detect the leading edge of the sheet by the registration sensor 131, for example, when the sheet is conveyed with the interval between the sheets being 0 or close to 0, or when the sheets are overlapped and conveyed. In this case, the sheets are conveyed at such intervals.

  In the first embodiment, the registration unit 1 is configured so that the registration sensor 131 can detect the leading edge of the sheet even when the registration sensor 131 conveys the sheet at an interval such that the registration sensor 131 cannot detect the leading edge of the sheet. That is, the registration sensor 131 is offset, the sheet is offset when the registration unit 1 conveys the sheet, and after the leading edge of the sheet is detected by the registration sensor 131, the registration unit 1 detects the sheet S in a direction opposite to the offset direction. Shifting.

  Hereinafter, a specific configuration of the resist unit 1 will be described with reference to FIG.

  As shown in FIG. 2, the assist roller pair 10 includes an assist drive roller 10a and an assist driven roller 10b that is in pressure-contact with the assist drive roller 10a by a pressure spring (not shown) so as to be separated. Here, the assist drive roller 10a is rotationally driven in the sheet conveyance direction by the assist motor 11, and can be offset by the assist shift motor 12 in the width direction orthogonal to the sheet conveyance direction integrally with the assist driven roller 10b. . Therefore, the assist roller pair 10 can sandwich and convey the sheet S by driving the assist motor 11. The assist roller pair 10 can offset the sheet S in the offset direction parallel to the width direction orthogonal to the sheet conveyance direction by driving the assist shift motor 12 while conveying the sheet S.

  Further, the assist driven roller 10b is moved in a direction away from the assist driving roller 10a by the assist release motor 14, and the nipping of the sheet S can be released.

  In FIG. 2, an assist shift HP sensor 13 for detecting the home position (HP) of the assist driving roller 10a is disposed in the vicinity of the assist driving roller 10a. An assist release HP sensor 15 for detecting the home position of the assist driven roller 10b is disposed in the vicinity of the assist driven roller 10b.

  The skew feeding correction roller pairs 21 and 22 constitute a skew feeding correcting portion that corrects the skew feeding of the sheet S while conveying the sheet S, and is arranged at a predetermined interval L on both sides in the width direction. .

  The skew correction roller pair 21 and 22 includes skew correction drive rollers 21a and 22a formed in a C shape with a part of the peripheral surface cut away. Further, the skew correction roller pair 21 and 22 has skew correction driven rollers 21b and 22b that are in pressure contact with the skew correction drive rollers 21a and 22a by a pressure spring (not shown).

  The skew correction driving rollers 21a and 22a are independently driven in the sheet conveying direction by skew correction motors 23 and 24, respectively. As a result, the sheet S is conveyed while being sandwiched between the skew correction driving rollers 21a and 22a and the skew correction driven rollers 21b and 22b.

  An activation sensor 27 for activating the skew correction motors 23 and 24 is disposed upstream of the pair of skew correction rollers 21 and 22 in the sheet conveyance direction, and the skew correction is performed in synchronization with the detection of the leading edge of the sheet S. The motors 23 and 24 are started. The activation sensor 27 is offset in the width direction from the reference conveyance area of the horizontal path 110 in which the sheet S is conveyed in a state where the conveyance reference of the sheet S is matched with the image reference of the image (toner image) on the photosensitive drum 112. It is arranged at the position. That is, when the sheet S is offset in the width direction, the tip of the offset portion in the sheet S is disposed at a position where it can be detected.

  Here, as shown in FIG. 8, which will be described later, the skew correction driving rollers 21a and 22a have a home position where a portion where the peripheral surface is notched faces the skew correction driven rollers 21b and 22b. Then, the sandwiching of the sheet S is released. Further, by releasing the clamping of the sheet S in this way, the skew feeding correction roller pair 21 and 22 are prevented from hindering the conveyance of the sheet S and the shift in the width direction of the sheet S by the registration roller pair 30 described later. Can do.

  In FIG. 2, reference numerals 25 and 26 denote skew correction HP sensors for detecting the phases of the skew correction drive rollers 21a and 22a. The skew correction HP sensors 25 and 26 are used to detect the skew correction drive rollers. It is detected that 21a and 22a have moved to the home position.

  A line sensor 28 capable of detecting a side edge position (lateral registration position) in the width direction of the sheet S is disposed on the upstream side in the sheet conveyance direction of the pair of skew correction rollers 21 and 22. A line sensor 35 capable of detecting the side edge position of the sheet S is disposed on the downstream side in the sheet conveyance direction of the pair of skew correction rollers 21 and 22. Each of the line sensors 28 and 35 is formed in a strip shape extending in the width direction orthogonal to the sheet conveyance direction, and an axis (not shown) of the photosensitive drum 112 (see FIG. 1) provided on the downstream side in the sheet conveyance direction. Are arranged in parallel with each other.

  The registration roller pair 30 includes a registration driving roller 30a formed in a C shape with a part of the peripheral surface cut away, and a registration driven roller 30b pressed against the registration driving roller 30a by a pressure spring (not shown). It is configured.

  The registration driving roller 30a of the registration roller pair 30 is driven by the registration motor 31 in the sheet conveying direction. As a result, the sheet S is conveyed while being sandwiched by the registration roller pair 30 (the registration driving roller 30a and the registration driven roller 30b).

  Here, as shown in FIG. 5 to be described later, when the registration driving roller 30a is at the home position where the peripheral surface is cut away from the registration driven roller 30b, the nipping of the sheet S is released. Is done. Then, by releasing the nipping of the sheet S in this way, it is possible to prevent the registration roller pair 30 from interfering with the skew correction of the sheet S by the skew correction roller pair 21 and 22.

  The registration roller pair 30 is shifted in the width direction by a registration shift motor 33. As a result, the sheet S is shifted so that the conveyance reference in the width direction of the sheet S matches the image reference in the width direction of the image (toner image) formed on the photosensitive drum 112 of the image forming unit 1003. be able to. In FIG. 2, reference numeral 32 denotes a registration HP sensor for detecting the phase of the registration driving roller 30a. The registration HP sensor 32 detects that the registration driving roller 30a has moved to the home position.

  A registration shift HP sensor 34 detects the home position of the registration roller pair 30 in the width direction. The registration shift HP sensor 34 detects that the registration roller pair 30 has moved to the home position.

  Further, a registration sensor 131 serving as a leading edge detection unit for detecting the leading edge of the sheet S is disposed on the downstream side in the sheet conveyance direction of the registration roller pair 30 and in the vicinity of the registration roller pair 30. The registration sensor 131 is offset in the width direction from the reference conveyance area of the horizontal path 110 in which the sheet S is conveyed in a state in which the conveyance reference of the sheet S matches the image reference of the image (toner image) on the photosensitive drum 112. It is arranged at the position. That is, when the sheet S is offset in the width direction, the tip of the offset portion in the sheet S is disposed at a position where it can be detected. The assist roller pair 10 and the skew correction roller pairs 21 and 22 constitute a transport unit that can transport the succeeding sheet in an offset state with respect to the preceding sheet in the width direction. That is, the sheet S is offset by the assist roller pair 10 in the width direction and the skew correction is corrected by the skew correction roller pairs 21 and 22, and the sheet S is corrected by the assist roller pair 10 and the skew correction roller pairs 21 and 22. Transport in the offset state.

  The detection signals (detection information) from the sensors are input to the CPU 121 shown in FIG. 3 provided in the controller 120 (see FIG. 1), and the CPU 121 drives the motor and the like based on the detection signals from the sensors. I try to control it.

  Here, after the leading edge of the sheet S is detected by the registration sensor 131, the side end position (lateral registration position) in the width direction is detected by the line sensor 35. Then, based on the detection result of the line sensor 35, the sheet S is shifted in the width direction by the registration roller pair 30 so that the conveyance reference of the sheet S matches the image reference of the image (toner image) on the photosensitive drum 112. Is done. Then, based on the detection result of the registration sensor 131, the leading edge of the sheet S and the leading edge of the image (including the blank portion) on the photosensitive drum 112 are synchronized.

  FIG. 4 is a flowchart showing an outline of the operation of the registration unit 1. FIG. 5 is a schematic operation explanatory diagram when the resist unit 1 is viewed from the front. FIG. 6 is a schematic operation explanatory diagram when the resist unit 1 is viewed in plan. FIG. 7 is a diagram for explaining the motor operation in the registration unit 1. FIG. 8 is a schematic operation explanatory diagram when the resist unit 1 is viewed from the front. FIG. 9 is a schematic operation explanatory diagram when the resist unit 1 is viewed in plan. FIG. 10 is a diagram for explaining the motor operation in the registration unit 1. Hereinafter, the operation in the resist unit 1 will be described in detail along the flowchart of FIG. 4 with reference to FIGS.

  The sheet S fed from the cassette 100 is conveyed to the assist roller pair 10 by the vertical pass roller pair 105. When the sheet S reaches the assist roller pair 10, the CPU 121 first separates the vertical pass roller pair 105 by a roller release motor (not shown) as necessary for each size of the sheet S to release the nip of the vertical pass roller pair 105. (Step 1).

Next, as shown in FIGS. 6A and 6B, when the trailing edge of the preceding preceding sheet S ′ is removed from the line sensor 28, the width direction side of the sheet S at the position S <b> 1 of the succeeding succeeding sheet S. The end position (lateral registration position) is detected by the line sensor 28. Further, the side edge position of the sheet S in the position S2 of the sheet S when the distance [Delta] L ₁ conveyed in the sheet conveying direction from the position S1 of the sheet S is detected by the line sensor 28. Then, the CPU 121 calculates the deviation amount ΔL ₂ of the sheet S when the sheet S is conveyed by the distance ΔL ₁ based on the position S1 of the sheet S and the side edge position of the sheet S at the position S2. The skew amount is detected (step 2).

  Then, the CPU 121 activates the assist shift motor 12 and moves the assist roller pair 10 in the offset direction (arrow A direction in FIG. 6A) parallel to the width direction by the assist shift motor 12 (step 3). As a result, the succeeding sheet S sandwiched between the assist roller pair 10 is offset (shifted to the leading end position detection position) in the offset direction to the position S3 shown in FIG. 6C with respect to the preceding sheet S ′. Here, in FIG. 6A, the preceding sheet S ′ has already been shifted in the width direction by the registration roller pair 30 in the direction opposite to the offset direction, and the conveyance reference (center) C2 of the preceding sheet S ′ is the photosensitive drum. 112 matches the image reference (center) C1 of the image (toner image).

When the start sensor 27 detects the leading edge of the succeeding sheet S (step 4: Yes), the CPU 121 starts the motor 23 corresponding to the preceding side of the leading edge of the sheet S among the skew feeding correction motors 23 and 24. To do. Next, the delayed motor 24 is started after time Δt ₁ (step 5). Then, CPU 121 controls to the conveying speed _V L of the sheet S by the respective motors 23, 24, _{V R} is the velocity _{V 0.} In this way, the skew feeding correction roller activation control is executed in step 1 to step 5.

The time Δt ₁ is obtained by the following relational expression.

  As a result, the pair of skew correction rollers 21 and 22 whose roller nip has been released at the home position rotate in the direction of arrow B in FIG. 5, the sheet S is nipped and conveyed, and the skew correction operation starts.

Next, the deceleration amount of the conveyance speed _VL of the skew correction motor 23 is ΔV ₁ , the deceleration amount of the conveyance speed V _ASX of the assist motor 11 is ΔV ₂ , and the acceleration amount of the movement speed V _ASY of the assist shift motor 12 is ΔV _3. Then, each acceleration / deceleration amount is obtained by the following relational expression. The assist shift motor 12 is moved in the direction opposite to the offset direction.

Here, L _AS in the above relational expression is a distance in the sheet conveying direction between the assist roller pair 10 and the skew feeding correction roller pairs 21 and 22, and L _RP is the skew feeding roller pair 21 and the skew feeding correction roller. This is the distance in the width direction perpendicular to the sheet conveying direction with the pair 22.

  Then, the CPU 121 calculates the control amount of each motor, specifically, the deceleration amount of each of the motors 23 and 11 and the acceleration amount of the motor 12 (that is, various control parameters for performing skew correction) (step 6). .

As shown in FIG. 7, in the first skew correction section (T ₁ ), the CPU 121 reduces the conveyance speed V _L of the skew correction motor 23 from the speed V ₀ by the acceleration a ₁ by ΔV _{1 and} assists at the same time. The conveyance speed V _ASX of the motor 11 is decelerated by ΔV ₂ at an acceleration a ₂ from the speed V ₀ . At the same time, the CPU 121 accelerates the moving speed V _ASY of the assist shift motor 12 to ΔV ₃ with the acceleration a ₃ . The transport speed V _R of the skew correction motor 24, the speed V _0, acceleration and deceleration amount is zero.

Next, the CPU 121 re-accelerates the conveyance speeds V _L and V _ASX of the skew correction motor 23 and the assist motor 11 to the speed V ₀ at the end of the skew correction section (T ₁ ), and moves the assist shift motor 12 to the skew correction section. Stop at the end of (T ₁ ) (step 7). Thus, the first skew correction control is performed. At this time, the roller phases of the skew correction driving rollers 21a and 22a are the same. As a result, as shown in FIG. 6D, the sheet S that has been largely skewed as in the position S4 is corrected in skew as in the position S5.

Next, after the first skew correction control of the sheet S is completed, the conveyance speeds V _L , V _R , and V _ASX by the skew correction motors 23 and 24 and the assist motor 11 are changed from the speed V ₀ to the speed V ₀ ′. Decelerated.

Then, the CPU 121 causes the line sensor 28 and the line sensor 35 to detect the deviation amount ΔL ₄ of the sheet S as illustrated in FIG. 6E, so that the distance ΔL ₃ and the deviation amount ΔL between the line sensors 28 and 35 are detected. ₄ , the skew amount of the sheet S is detected (Step 8).

Next, similarly to the first skew correction control, the second skew correction control is performed. Therefore, the control amount of each motor, specifically, the deceleration amount of the conveyance speed _VL of the skew correction motor 23 is determined. ΔV ₁ ′ and the deceleration amount ΔV ₂ ′ of the conveyance speed V _ASX of the assist motor 11 are calculated. Further, an acceleration amount ΔV ₃ ′ of the moving speed V _ASY of the assist shift motor 12 is calculated (step 9).

Next, CPU 121, in the second round of skew correction interval _{(T 2),} [Delta] V ₁ 'decelerates the conveying velocity _{V L} of the skew correction motor 23' acceleration _{a 1} from the 'speed _{V 0,} at the same time assist motor 11 transport speed V _ASX is decelerated from speed V ₀ ′ by acceleration a ₂ ′ by ΔV ₂ ′. At the same time, the CPU 121 accelerates the moving speed V _ASY of the assist shift motor 12 to ΔV ₃ ′ with acceleration a ₃ ′. Then, CPU 121 is skew correction motor 23 and the assist motor 11 the skew correction interval _{(T 2)} and re-accelerated to the speed _{V 0} 'at the end, stops the assist shift motor 12 to the skew correction interval _{(T 2)} at the end (Step 10). Thereby, the second skew correction control is performed, and the skew of the sheet S is completely corrected to the position S6 as shown in FIG.

  Next, the CPU 121 conveys the sheet S whose skew state has been corrected by the skew correction roller pair 21 and 22 to the registration roller pair 30 and starts the registration motor 31 (step 11, registration roller start control).

  As a result, the registration roller pair 30 whose roller nip is released at the home position rotates in the direction of arrow B shown in FIG. 8, and the sheet S is conveyed. When the sheet S is nipped by the registration roller pair 30, the CPU 121 releases the roller nip of the skew correction roller pair 21 and 22 as shown in FIG. 8 based on the skew correction HP sensors 25 and 26, respectively. Stop at the home position (step 12). In this way, the skew correction roller HP stop control is executed at step 12.

  Next, the CPU 121 determines whether or not the registration sensor 131 has detected the leading edge of the sheet S that is conveyed offset in the offset direction (step 13). That is, since the succeeding sheet S is conveyed with an offset in the offset direction with respect to the preceding sheet S ′, the registration sensor 131 detects the leading end St of the offset portion Sa (shaded portion in FIG. 9) of the sheet S. Can do.

  When the registration sensor 131 is turned on (detects the leading edge of the sheet S) (step 13: Yes), simultaneously with the detection by the registration sensor 131, the side edge position (lateral registration position) of the sheet S is detected by the line sensor 35 ( step 14). In this way, the front registration lateral registration detection is executed at step 13 and step 14.

Next, as shown in FIG. 10, the CPU 121 calculates a time difference Δt ₃ between the detection timing of the registration sensor 131 and the timing (ITOP) when the photosensitive drum 112 is irradiated with laser light. Here, it is assumed that the distance from the exposure position 112a of the photosensitive drum 112 to the transfer portion 112b is l ₀ , and the distance from the registration sensor 131 to the transfer portion 112b is l ₁ (see FIG. 1). Next, based on the time difference Δt ₃ , the CPU 121 synchronizes (matches) the leading edge of the image on the photosensitive drum 112 that rotates and moves the distance l ₀ with the leading edge of the sheet S that is conveyed the distance l _1. The deceleration amount ΔV ₄ and the shift time T ₃ of _{31 and 11} are calculated (step 15).

Further, the CPU 121 calculates the acceleration amount ΔV ₅ and the shift time T ₄ in the shift direction (the direction opposite to the offset direction) of each of the motors 33 and 12 based on the detection signal of the line sensor 35 (step 16).

  The CPU 121 controls the registration motor 31, the registration shift motor 33, the assist motor 11 and the assist shift motor 12 to synchronize (match) the image (toner image) on the photosensitive drum 112 and the sheet S ( step 17). In this way, the front registration lateral registration correction control is executed in steps 15 to 17.

  Further, based on the side edge position of the sheet S detected by the line sensor 35, the CPU 121 sets the sheet S conveyance reference (center) C2 to the image reference (center) C1 of the image (toner image) on the photosensitive drum 112. The sheets S are shifted in the shift direction so as to match. In other words, the CPU 121 controls the registration roller pair 30 to shift the sheet S to a position where the sheet S is conveyed based on the central reference. By shifting the sheet S by the registration roller pair 30 in this way, the side edge of the preceding sheet S ′ and the side edge of the succeeding sheet S are aligned.

  Further, based on the detection result of the registration sensor 131, the CPU 121 conveys the registration roller pair 30 so that the leading edge of the image (toner image) on the photosensitive drum 112 and the leading edge of the sheet S are synchronized (matched). Control to change the speed.

  Next, when the shift operation of the sheet S is completed, the assist release motor 14 is rotated forward to release the pressure contact between the assist driven roller 10b and the assist drive roller 10a of the assist roller pair 10 (step 18).

  When the nip release of the assist roller pair 10 is detected by the assist release HP sensor 15, the assist shift motor 12 is activated to shift the assist roller pair 10 to the home position. Thereafter, when the assist shift HP sensor 13 detects (OFF) the assist roller pair 10 that has been shifted, the assist shift motor 12 is stopped (step 19).

At this time, since the assist roller pair 10 is moving in the shift direction by the tip detection shift, the first skew correction, and the second skew correction and the lateral registration correction, the assist roller motor 12 is driven at the maximum moving speed at which the assist shift motor 12 can be driven. T ₅ (FIG. 10) shifts.

  The assist roller pair 10 is nipped again by the assist release motor 14 at a position where the trailing edge of the sheet S passes through the assist roller pair 10 (step 20). In this way, pre-registration HP control is executed in steps 17 to 20.

  A toner image is transferred to the sheet S conveyed by the registration roller pair 30 by the photosensitive drum 112, and the registration motor 31 operates in a state where the nip by the rollers of the registration roller pair 30 is released with reference to the registration HP sensor 32. Stop (step 21). At the same time, the registration shift motor 33 is started, shifts to the home position, and stops when the registration shift HP sensor 34 is detected (step 22). In this way, registration roller HP stop control is executed at step 21 and step 22. The above step 1 to step 22 are repeated.

  As described above, according to the first embodiment, the assisting roller pair 10 offsets the succeeding sheet S from the preceding sheet S ′ in the offset direction parallel to the width direction. As a result, the leading end St of the offset portion Sa of the subsequent sheet S can be detected by the registration sensor 131.

  Therefore, when the sheets are continuously conveyed, the registration sensor 131 can detect the leading edge St of the succeeding sheet S with high accuracy. As a result, the image position on the photosensitive drum 112 and the sheet S can be continuously aligned with high accuracy. In addition, since the offset sheet is conveyed by the skew correction roller pair 21 and 22, the skew is corrected, the detection accuracy of the leading edge St by the registration sensor 131 is further improved.

  In this embodiment, the sheet is shifted to the conveyance reference after the sheet is offset and the leading edge is detected. However, the sheet may be conveyed to the image forming unit in an offset state without being shifted. In this case, the image forming unit may perform image formation by adjusting the image forming position in accordance with the position of each sheet.

  That is, the subsequent sheet is shifted with respect to the preceding sheet by alternately offsetting the sheet in the direction orthogonal to the sheet conveying direction, and the leading edge of the subsequent sheet is detected at the shifted position. Further, the method of offsetting the sheet is not limited to this, and every other continuously conveyed sheet is shifted in a direction perpendicular to the sheet conveying direction, and the subsequent sheet is offset with respect to the preceding sheet. Also good. Furthermore, even when successive sheets are offset in the same direction in the direction orthogonal to the sheet conveying direction, the preceding sheet can be changed by alternately changing the offset amount between the first value and the second value. The subsequent sheet may be offset with respect to. That is, in either case, the preceding sheet and the succeeding sheet are conveyed while being shifted in a direction perpendicular to the sheet conveying direction. In these cases, it is necessary to provide registration sensors for detecting the leading edge of the sheet at a plurality of locations corresponding to the portions where the preceding sheet and the succeeding sheet are displaced in the direction orthogonal to the sheet conveying direction. Further, a side edge position detecting unit that detects the position of the offset side edge of the sheet is provided, and the image writing position in the main scanning direction on the photosensitive drum 112 is adjusted according to the detected position of the side edge of the sheet. That is, the position of the latent image formed on the photosensitive drum 112 is adjusted according to the position of each sheet. Thereby, the position of the sheet and the image in the width direction of the sheet can be matched.

[Second Embodiment]
In the first embodiment, a case where the image forming apparatus is applied to a so-called active resist type image forming apparatus has been described. In the second embodiment, a case where the image forming apparatus is applied to a so-called skew feeding image forming apparatus will be described. In addition, about the same structure as the said 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 11 is an explanatory diagram illustrating an outline of a configuration of a registration unit of a printer which is an example of an image forming apparatus including a sheet conveying device according to the second embodiment of the present invention.

  In the second embodiment, the registration unit 1 ′ includes an assist roller pair 10 that is rotationally driven by the assist motor 11, and a registration roller pair 30 that is rotationally driven by the registration motor 31 and shifted in the width direction by the registration shift motor 33. And.

  The registration unit 1 ′ is provided between the assist roller pair 10 and the registration roller pair 30 and includes a plurality of skew feeding rollers 401 that are rotationally driven by a skew feeding motor 402. Further, the registration unit 1 ′ is provided on a side in the width direction of the skew feeding roller 401, and includes a side end guide 403 that guides the side edge in the width direction of the sheet S.

  The skew feeding roller 401 is arranged to be inclined at a predetermined angle with respect to the sheet conveyance direction, and conveys the sheet S while offset to the side end guide 403 side. The side end guide 403 is formed to extend in parallel with the sheet conveyance direction, and a side end of the sheet S conveyed to the skew feeding roller 401 comes into contact therewith. Thereby, the posture of the sheet S is corrected, and the skew of the sheet S is corrected.

  That is, the skew feeding roller 401 and the side end guide 403 constitute a conveyance unit that can convey the succeeding sheet S in an offset state parallel to the width direction with respect to the preceding sheet S ′.

  Then, the succeeding sheet S is conveyed while being offset in the offset direction by the skew feeding roller 401 and the side end guide 403, and the leading end St of the offset portion Sa is detected by the registration sensor 131. Next, the succeeding sheet S is shifted in the direction opposite to the offset direction by the registration roller pair 30. As a result, the conveyance reference (center) of the sheet S matches the image reference (center) of the image (toner image) on the photosensitive drum. Based on the detection result of the registration sensor 131, the conveyance speed of the sheet S is controlled so that the leading edge of the image on the photosensitive drum and the leading edge of the sheet S are synchronized.

  As described above, also in the second embodiment, as in the first embodiment, the registration sensor 131 can detect the leading edge St of the succeeding sheet S with high accuracy. As a result, the image position on the photosensitive drum 112 and the sheet S can be continuously aligned with high accuracy.

[Third Embodiment]
In the first embodiment and the second embodiment, the case where the sheet is offset in the width direction during the conveyance of the sheet has been described. However, in the third embodiment, the sheet is offset in advance and the offset is performed. A case where a sheet is conveyed will be described. In addition, about the structure same as the said 1st, 2nd embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  FIG. 12 is an explanatory diagram illustrating an outline of a main configuration of a printer that is an example of an image forming apparatus including a sheet conveying device according to a third embodiment of the present invention.

  In the third embodiment, the cassette 100 as the sheet storage unit is previously offset and arranged in an offset direction parallel to the width direction. Then, the sheet S that has been offset in advance by the cassette 100 is conveyed by a conveyance unit 10 ′ configured by a pair of conveyance rollers and the like.

  Then, the leading end St of the offset portion Sa of the sheet S that is offset with respect to the preceding sheet is detected by the registration sensor 131 and shifted in the direction opposite to the offset direction by the registration roller pair 30.

  As described above, in the third embodiment, the same effect as that of the above-described embodiment can be obtained, and the control for offsetting the sheet S can be omitted by offsetting the cassette 100 in advance. Further, since a motor or the like for driving the roller pair in the offset direction in order to offset the sheet S can be omitted, the apparatus can be miniaturized.

  Here, when the present invention is applied to an image forming apparatus that forms images on both sides of the sheet S, the image formed sheet S may be offset by a path returning to the image forming unit.

  As mentioned above, although this invention was demonstrated based on the said 1st-3rd embodiment, this invention is not limited to this.

  In the above embodiment, the sheet conveyance speed is changed to synchronize the leading edge of the image on the photosensitive drum 112 and the leading edge of the sheet, but the timing for forming an image on the photosensitive drum 112 is changed, The leading edge of the image and the leading edge of the sheet may be synchronized.

  Further, in the above-described embodiment, a case has been described in which a sheet is transported with a center reference in which the center in the width direction as the sheet transport reference matches the center in the width direction as the image reference of the image on the photosensitive drum 112. It is not limited. In other words, the sheet may be conveyed on a one-side basis in which one side in the width direction of the sheet coincides with one side in the width direction of the image on the photosensitive drum 112.

  Further, the image reference of the image formed on the photosensitive drum 112 may be matched with the sheet conveyance reference. In this case, the shift amount to be shifted in the direction opposite to the offset direction by the registration roller pair 30 can be arbitrarily set. That is, the preceding sheet S ′ and the succeeding sheet S are not necessarily aligned, and an image (toner image) may be formed on the photosensitive drum 112 in accordance with the position of the sheet S.

1 is a schematic configuration diagram of a printer that is an example of an image forming apparatus including a sheet conveying device according to a first embodiment of the present invention. It is a figure explaining the structure of the resist part provided in the horizontal path | pass. It is a control block diagram of a resist part. It is a flowchart which shows the outline | summary of operation | movement of a registration part. FIG. 10 is a schematic operation explanatory diagram when a resist portion is viewed from the front. FIG. 10 is a schematic operation explanatory diagram when the resist portion is viewed in plan. (A) is a figure which shows the state which is conveying the subsequent sheet | seat by the assist roller pair, (b) is a figure which shows the state which has detected the side edge of the subsequent sheet | seat, (c), It is a figure which shows the state which offset the subsequent sheet | seat. (D) is a figure which shows the state which correct | amends skew feeding of the succeeding sheet | seat, (e) is a figure which shows the state which has detected the side edge of the succeeding sheet | seat. It is a figure explaining the motor operation | movement in a registration part. FIG. 10 is a schematic operation explanatory diagram when a resist portion is viewed from the front. FIG. 10 is a schematic operation explanatory diagram when the resist portion is viewed in plan. It is a figure explaining the motor operation | movement in a registration part. FIG. 10 is an explanatory diagram illustrating an outline of a configuration of a registration unit of a printer that is an example of an image forming apparatus including a sheet conveying device according to a second embodiment of the present invention. FIG. 10 is an explanatory diagram illustrating an outline of a main configuration of a printer that is an example of an image forming apparatus including a sheet conveying device according to a third embodiment of the present invention.

Explanation of symbols

10 Conveying unit, offset unit, conveying roller pair (assist roller pair)
10 'Conveying parts 21, 22 Conveying part (skew correction roller pair)
30 Shift section (registration roller pair)
100 Sheet storage (cassette)
1000 Image forming device (printer)
1003 Image forming unit 112 Image forming unit (photosensitive drum)
131 Tip detection unit (registration sensor)
401 Conveying section, offset section (slope feeding roller)
403 Transport section, offset section (side edge guide)

Claims (3)

An image forming apparatus comprising a sheet conveying device for conveying sequentially with undetectable interval sheet leading edge detecting unit, and an image forming unit for forming an image on a sheet conveyed by said sheet conveying device,
The sheet conveying device is
An offset unit for offsetting a subsequent sheet following the preceding preceding sheet in an offset direction perpendicular to the sheet conveyance direction;
A leading edge detector that detects a leading edge of an offset portion of the subsequent sheet when the subsequent sheet offset by the offset section is being conveyed ;
A shift unit that shifts the subsequent sheet detected by the leading edge detection unit in a direction orthogonal to the sheet conveyance direction and in a direction opposite to the offset direction;
Based on the detection result of the leading edge detection unit, the leading edge of the sheet and the leading edge of the image formed by the image forming unit are synchronized,
An image forming apparatus. Said offset portion is a pair of conveying rollers movable in the offset direction while nipping the sheet,
The image forming apparatus according to claim 1 . Said offset portion extends parallel to the sheet conveying direction, a side edge guide for guiding a side edge of the sheet, is disposed inclined with respect to the sheet conveying direction, those of the side edge of the sheet to the side edge guide A skew feeding roller that conveys in contact,
The image forming apparatus according to claim 1 .

Images