JP2012211002A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses skewing of a paper sheet.SOLUTION: The image forming apparatus controls a conveying mechanism as follows. When the paper sheet width of a paper sheet 3 to be conveyed is an A4 size, the sheet 3 is conveyed to an image forming unit 5 by registration rollers 14A and 14B while a conveying force to be transferred to the sheet by a multipurpose side supplying roller 15 is shut off after the skewing of the sheet 3 is corrected by the registration rollers 14A and 14B. When the paper sheet width of the paper sheet 3 to be conveyed is a postcard size, the sheet 3 is conveyed to the image forming unit 5 by the multipurpose side supplying roller 15 and the registration rollers 14A and 14B while the conveying force is transferred to the sheet 3 by the multipurpose side supply roller 15 even after the skewing of the sheet 3 is corrected by the registration rollers 14A and 14B.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus includes a registration roller pair that corrects skew of a sheet conveyed to an image forming unit that forms an image on a sheet, and a conveyance roller that conveys the sheet to the registration roller pair. Yes. For example, the image forming apparatus described in Patent Document 1 includes a pair of paper feed rollers and a registration roller. The paper feed roller feeds paper from the paper feed cassette toward the registration roller pair. The registration roller pair includes a driving roller and a driven roller, and the driving roller obtains a driving force through an electromagnetic clutch. The driven roller is rotatably supported by both bearings, and is pressed against the driving roller via the bearing by the action of a spring. Each bearing has a shaft hole at one end, and a shaft pin attached to the main body frame is rotatably fitted to form a fulcrum of the bearing. The spring is located between this fulcrum and the bearing hole in which the driven roller enters. Is engaged with the bearing and exerts a pressure contact force on it.

Japanese Patent Application Laid-Open No. 5-119637

  However, since the registration roller pair in the image forming apparatus described in Patent Document 1 is pressed at both ends of the driven roller, the conveyance force at the center of the registration roller pair in the sheet conveyance direction is weaker than the conveyance force at both ends. Tend to be. When a small size paper such as a postcard is transported, if the paper is transported by the central portion of the pair of registration rollers having a weak transport force, there is a problem that the skew of the paper occurs due to insufficient transport force.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of suppressing the skew of a sheet.

  In order to achieve this object, an image forming apparatus according to claim 1 includes a printing unit that prints an image on a sheet, a sheet whose width in a direction orthogonal to the sheet conveyance direction is a predetermined first width, and In the image forming apparatus including a transport mechanism that transports a paper having a second width smaller than the first width to the printing unit, the first roller that transports the paper and the paper transported by the first roller When the sheet width of the sheet to be conveyed is the first width and the skew of the sheet is corrected by the pair of registration rollers, the sheet is transmitted to the sheet by the first roller. When the conveying force is interrupted and the sheet is conveyed to the printing unit by the registration roller pair, and the sheet width of the conveyed sheet is the second width, the skew of the sheet is corrected by the registration roller pair. Later also said Is conveyed force is transmitted to the sheet by one roller, and a control unit for controlling the conveying mechanism so that the paper is conveyed to the printing section by the first roller and the resist roller pair.

  According to the image forming apparatus of the first aspect, when the sheet width of the conveyed sheet is the first width, the sheet is conveyed by the first roller until the skew of the conveyed sheet is corrected. . After the skew of the sheet is corrected, the conveying force transmitted to the sheet by the first roller is interrupted, and the conveying force is transmitted to the sheet by the registration roller pair. When the sheet width of the sheet to be conveyed is a second width that is narrower than the first width, the conveying force is transmitted to the sheet by the first roller even after the skew of the sheet is corrected. Since the sheet is conveyed by the two rollers of the registration roller pair and the first roller, the shortage of conveyance force in the registration roller pair is resolved. Therefore, skew of the paper can be suppressed.

  According to a second aspect of the present invention, the image forming apparatus includes a second roller capable of conveying the sheet conveyed by the registration roller pair, and the control unit has a sheet length in the conveyance direction of the conveyed sheet. When longer than the first sheet conveyance distance from one roller to the second roller, the sheet is conveyed by the first roller until the leading edge of the sheet reaches the second roller, and then the sheet is conveyed by the first roller. The transport mechanism is controlled so that the transport force transmitted to the motor is interrupted.

  According to the image forming apparatus of the second aspect, when the paper length in the transport direction of the transported paper is longer than the first paper transport distance from the first roller to the second roller, the leading edge of the paper becomes the second roller. The paper is conveyed by the first roller and the registration roller pair until it reaches. After the leading edge of the paper reaches the second roller, the paper can be conveyed by the registration roller pair and the second roller. Even before the leading edge of the paper reaches the second roller and after the leading edge of the paper reaches the second roller, the paper can be conveyed by at least two rollers. That is, after the leading edge of the paper reaches the second roller, the paper is transported by the registration roller pair and the two rollers of the second roller even if the transport force transmitted to the paper by the first roller is interrupted. Can do. Therefore, even if the conveying force transmitted to the sheet by the first roller after the leading edge of the sheet reaches the second roller, the shortage of the conveying force of the registration roller pair is resolved, so that the skew of the sheet can be suppressed. And the conveyance force transmitted to a sheet | seat by the 1st roller which became unnecessary can be suppressed.

  The image forming apparatus according to claim 3, wherein when the paper length in the transport direction of the transported paper is shorter than the first paper transport distance, the control unit sets the rear end of the paper to the first roller. The transport mechanism is controlled so that the transport force transmitted to the sheet by the first roller is cut off immediately before passing through the contact position.

  According to the image forming apparatus of the third aspect, the conveying force transmitted to the sheet by the first roller is interrupted immediately before the trailing end of the sheet to be conveyed passes through the contact position with the first roller. While the transported paper is transported by the first roller, the skew of the paper can be suppressed, and the paper can be transported without being double-fed.

  The image forming apparatus according to claim 4, further comprising: a paper width determining unit that determines whether a paper width of the conveyed paper is the first width or the second width, and the paper width The determination unit includes a sheet width sensor that detects the sheet width, and determines whether the sheet width of the sheet conveyed by the output of the sheet width sensor is the first width or the second width. to decide.

  According to the image forming apparatus of claim 4, even when a sheet with an unknown sheet width is conveyed, the sheet width sensor determines whether the sheet width is the first width or the second width. Therefore, it is possible to accurately execute the control for suppressing the skew of the sheet.

  The image forming apparatus according to claim 5, wherein the first roller has a second sheet conveyance distance from the first roller to the registration roller pair by a one-sheet conveyance operation of the first roller. If the paper width of the paper to be transported is the first width, the control unit stops the transport operation after the transport operation is performed once, and sets the paper width of the paper to be transported. In the case of the second width, the transport mechanism is controlled so that the transport operation is stopped after the transport operation is performed at least twice.

  According to the image forming apparatus of the fifth aspect, the conveyance distance of the sheet by one conveyance operation of the first roller is larger than the second sheet conveyance distance from the first roller to the registration roller pair. That is, when the conveyance operation of the first roller is performed once, the leading edge of the sheet is sandwiched between the registration roller pair. When the conveyance operation of the first roller is performed twice, the leading edge of the sheet passes the registration roller pair, and the sheet is conveyed by the two rollers of the first roller and the registration roller pair. Therefore, skewing of the paper can be easily suppressed by controlling the rotation speed of the first roller.

The image forming apparatus according to claim 6, wherein the first roller has a second paper conveyance distance from the first roller to the registration roller pair by a one-time conveyance operation of the first roller. The first roller and the paper are in contact with each other when the one transport operation is started, and the first roller and the paper are separated when the transport operation is finished,
When the sheet width of the sheet to be transported is the first width, the control unit stops the transport operation after the transport operation is performed once, and the sheet width of the sheet to be transported is the second width. In this case, the transport mechanism is controlled so that the transport operation is stopped after the transport operation is performed at least twice.

  According to the image forming apparatus of the sixth aspect, the conveyance distance of the sheet by one conveyance operation of the first roller is larger than the second sheet conveyance distance from the first roller to the registration roller pair. That is, when the conveyance operation of the first roller is performed once, the leading edge of the sheet is sandwiched between the registration roller pair, and then the first roller and the sheet are separated from each other, so that back tension applied to the sheet can be prevented. When the conveyance operation by the first roller is performed twice, the leading edge of the paper passes through the registration roller pair, and the paper is conveyed by two rollers, the first roller and the registration roller pair. Therefore, the skew of the sheet can be easily suppressed by controlling the number of times the first roller is transported.

  The image forming apparatus according to claim 7, wherein the control unit includes the registration roller until the conveying force transmitted to the paper by the first roller is interrupted from the time when the registration roller pair sandwiches the leading edge of the paper. Stop rotation of the pair.

  According to the image forming apparatus of the seventh aspect, if the sheet is conveyed by the registration roller pair while the conveying force transmitted to the sheet by the first roller is interrupted, the sheet may be skewed. On the other hand, by adjusting the rotation timing of the first roller and the registration roller pair, it is possible to suppress the skew of the sheet that occurs while the conveying force transmitted to the sheet by the first roller is interrupted.

  The image forming apparatus according to claim 8, wherein the registration roller pair includes a driving roller and a driven roller, and at least one of the driving roller or the driven roller is rotatably supported by two bearings, The distance from the position where one of the two bearings is arranged to the position where the other bearing is arranged is the second width by being pressed against the other roller via the two bearings by the action of a spring. Bigger than.

  According to the image forming apparatus of claim 8, the distance from the position where one of the two bearings is disposed to the position where the other bearing is disposed is larger than the second width, and the driving roller or the driven Since at least one of the rollers is pressed against the other roller via two bearings by the action of a spring, at least one of the rollers bends. That is, the conveyance force of the registration roller pair near the center of the two bearings is weaker than the conveyance force of the registration roller pair near the bearings. Therefore, it is more suitable when the second width paper is conveyed by the registration roller pair.

  According to the present invention, it is possible to suppress sheet skew.

1 is a side sectional view showing an overall internal configuration of a laser printer according to a first embodiment of the present invention. It is a conceptual diagram showing the width relationship between the registration roller and the paper according to the first embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of a laser printer according to a first embodiment of the present invention. 6 is a timing chart (part 1) illustrating an operation when printing on a paper on a multi-purpose tray according to the first exemplary embodiment of the present invention. 6 is a timing chart (part 2) illustrating an operation when a sheet on a multi-purpose tray according to the first embodiment of the present invention is printed. 4 is a flowchart showing a flow of processing when a sheet on a multi-purpose tray according to the first embodiment of the present invention is printed. It is a block diagram showing the electric constitution of the laser printer which concerns on the 2nd Embodiment of this invention. 10 is a timing chart illustrating an operation when a sheet on a multi-purpose tray according to the second embodiment of the present invention is printed. 10 is a flowchart showing a flow of processing when a sheet on a multi-purpose tray according to the second embodiment of the present invention is printed. 10 is a timing chart showing an operation when a sheet on a multi-purpose tray according to a third embodiment of the present invention is printed. 10 is a flowchart illustrating a flow of processing when a sheet on a multi-purpose tray according to a third embodiment of the present invention is printed. It is a timing chart showing the operation | movement when the paper on the multipurpose tray which concerns on the 4th Embodiment of this invention is printed. 10 is a flowchart illustrating a processing flow when a sheet on a multi-purpose tray is printed according to a fourth embodiment of the present invention.

[First Embodiment]
Next, a first embodiment of the present invention will be described with reference to FIGS. In the first embodiment, a case where the present invention is applied to a laser printer will be described.

(Whole structure of laser printer)
FIG. 1 is a side sectional view showing the overall internal configuration of the laser printer according to the first embodiment of the present invention. FIG. 2 is a conceptual diagram showing the width relationship between the registration roller and the sheet according to the first embodiment of the present invention. The laser printer 1 includes a main body casing 2, a paper feeding unit 4 for feeding paper 3 into the main body casing 2, an image forming unit 5 for forming an image on the fed paper 3, and the like. It has. In the following description, the left side of FIG. 1 is the front and the right side is the rear. The laser printer 1 according to this embodiment is an example of an image forming apparatus according to the present invention. The image forming unit 5 of the present embodiment is an example of a printing unit of the present invention.

(1) Main Body Casing An attachment / detachment opening 6 for attaching / detaching a process cartridge 26 described later is formed on the front upper surface of the main body casing 2, and the attachment / detachment opening 6 is covered with a front cover 7 so as to be opened and closed. Further, on the upper surface of the main casing 2, a paper discharge tray 9 on which the paper 3 after image formation is stacked is provided.

(2) Paper Feed Unit The paper feed unit 4 includes a paper feed tray 11 that is detachably attached to the bottom of the main body casing 2, a paper pressing plate 16 provided in the paper feed tray 11, and a paper feed tray. 11 with respect to the paper feed roller 13 and the separation pad 12 provided above one end of the paper 11, the transport rollers 18 and 19 provided on the downstream side of the paper feed roller 13 in the transport direction of the paper 3, and the transport rollers 18 and 19. Registration rollers 14 </ b> A and 14 </ b> B provided on the downstream side in the conveyance direction of the sheet 3 are provided, and the sheet 3 loaded on the sheet feeding tray 11 is supplied to the image forming unit 5. Hereinafter, the upstream side or the downstream side in the conveyance direction of the sheet 3 may be simply referred to as the upstream side or the downstream side. The registration rollers 14A and 14B of this embodiment are a registration roller pair of the present invention.

  The paper pressing plate 16 can stack the papers 3 in a stacked manner, and is supported so as to be swingable at the far end with respect to the paper feed roller 13, thereby moving the near end up and down. It is possible to be biased upward by a spring (not shown) from the back side. Therefore, the paper pressing plate 16 is swung downward against the urging force of the spring with the end far from the paper feeding roller 13 as a fulcrum as the amount of paper 3 loaded increases. The paper feed roller 13 and the separation pad 12 are disposed to face each other, and the separation pad 12 is pressed toward the paper feed roller 13 by a spring 17 disposed on the back side of the separation pad 12. The uppermost sheet 3 on the sheet pressing plate 16 is pressed toward the sheet feeding roller 13 by a spring (not shown) from the back side of the sheet pressing plate 16, and the sheet feeding roller 13 and the separation pad are rotated by the rotation of the sheet feeding roller 13. After being sandwiched between 12 sheets, the sheets are fed one by one. The fed paper 3 is sent to the registration rollers 14A and 14B by the transport rollers 18 and 19. The registration rollers 14A and 14B are composed of a pair of rollers, and send the paper 3 to the image forming unit 5 after a predetermined registration.

  The paper feed unit 4 includes a multipurpose tray 14 that can be opened and closed at the front of the main casing 2, a guide 65 that regulates the width of the paper 3 stacked on the multipurpose tray 14, A paper width detection sensor 64 for detecting the width, a multi-purpose side feed roller 15 for feeding the paper 3 stacked on the multi-purpose tray 14 and a multi-purpose side separation pad 15a are provided. The side paper feed roller 15 and the multi-purpose side separation pad 15a are arranged opposite to each other, and the multi-purpose side separation pad 15a is arranged on the multi-purpose side by a spring (not shown) arranged on the back side of the multi-purpose side separation pad 15a. It is pressed toward the paper feed roller 15. The paper 3 stacked on the multi-purpose tray 14 is regulated in width by a guide 65 and is sandwiched between the multi-purpose side feed roller 15 and the multi-purpose side separation pad 15 a by the rotation of the multi-purpose side feed roller 15. After that, the sheets are fed one by one. The fed paper 3 is sent to the image forming unit 5 via the registration rollers 14A and 14B. As shown in FIG. 2, for example, when a postcard-size paper 3 is placed on the multi-purpose tray 14, the guide 65 illustrated by a one-dot chain line is directed toward the center in the width direction of the paper 3. Then, it is moved to the position of the guide 65 shown by the two-dot chain line in the direction of the arrow, and the width of the sheet 3 is regulated. When the A4 size paper 3 is placed, the width of the paper 3 is regulated at the position of the guide 65 illustrated by the one-dot chain line. The paper width detection sensor 64 detects the width of the guide 65 that regulates the width of the paper 3 provided on the multipurpose tray 14. The multi-purpose-side paper feed roller 15 of this embodiment is an example of the first roller of the present invention.

  The transport path from the paper feed tray 11 to the registration rollers 14A and 14B and the transport path from the multi-purpose tray 14 to the registration rollers 14A and 14B merge above the paper feed rollers 13. A pre-registration sensor 21 that detects the presence or absence of the sheet 3 is provided in the vicinity of the junction, and registration rollers 14A and 14B are disposed on the downstream side thereof. The registration rollers 14A and 14B include a registration roller 14A that is rotationally driven, and a registration roller 14B that is driven to rotate in pressure contact with the upper side of the registration roller 14A. A post-registration sensor 22 that detects the presence or absence of the sheet 3 is provided on the downstream side of the registration rollers 14A and 14B. Further, on the downstream side of the post-registration sensor 22, a photosensitive drum 31 and a transfer roller 34 included in an image forming unit 5 described later are disposed to face each other. When the sheet 3 conveyed by the registration rollers 14A and 14B passes through a transfer position between the photosensitive drum 31 and the transfer roller 34, the toner image on the photosensitive drum 31 is transferred onto the sheet 3. . The photosensitive drum 31 of this embodiment is an example of the second roller of the present invention. The registration roller 14A of this embodiment is an example of the driving roller of the present invention. The registration roller 14B of this embodiment is an example of a driven roller of the present invention.

  As shown in FIG. 2, the registration roller 14A is rotatably supported at both ends of the registration roller 14A by bearings 14C and 14D. The bearing 14C is pressed in the direction in which the registration roller 14A is pressed against the registration roller 14B by the action of the spring 14E disposed on the frame 2A. The frame 2A is fixed inside the main casing 2. Similarly, the bearing 14D receives a force in a direction in which the registration roller 14A is pressed against the registration roller 14B by the action of a spring 14F disposed on the frame 2A. The registration roller 14 </ b> B is rotatably supported by a bearing (not shown) whose both ends are fitted to the main body casing 2. The registration roller 14A bends because both ends are pressed. Accordingly, the conveying force for conveying the sheet 3 near the center of the registration roller 14A is weaker than the conveying force near the bearings 14C and 14D. A distance L1 from the bearing 14C to the bearing 14D in the axial direction of the registration roller 14A is provided in order to transport the A3 size sheet 3 having the sheet width L2. When a sheet 3 narrower than the sheet width L3 of the postcard size for the A4 size is fed, the sheet 3 is conveyed near the center of the registration roller 14A having a weak conveyance force, so that the sheet 3 is conveyed only by the registration rollers 14A and 14B. The sheet 3 may be skewed.

  The rotation of the registration roller 14A is controlled by a registration roller solenoid 61 described later. The registration roller solenoid 61 is provided as a clutch mechanism between a main motor 60 and a registration roller 14A, which will be described later. When the power is off, the power is transmitted from the main motor 60 to the registration roller 14A. Transmission is cut off.

  The rotation of the multi-purpose side feed roller 15 is controlled by a feed roller electromagnetic clutch 62 described later. The electromagnetic clutch 62 for the feed roller is provided as a clutch mechanism between the main motor 60 and the multi-purpose feed roller 15, and power is transmitted from the main motor 60 to the multi-purpose feed roller 15 when turned on. When it is off, the power transmission is cut off. When the power transmission is interrupted, the multi-purpose-side paper feed roller 15 rotates with the conveyance of the paper 3. The registration rollers 14A and 14B, the multi-purpose side paper supply roller 15, the registration roller solenoid 61, and the paper supply roller electromagnetic clutch 62 of this embodiment are examples of the transport mechanism of the present invention.

(3) Image Forming Unit The image forming unit 5 includes a scanner unit 25, a process cartridge 26, a fixing unit 27, and the like.

(A) Scanner Unit The scanner unit 25 is provided in the upper part of the main casing 2 and includes a laser light source (not shown), a polygon mirror 29 that is driven to rotate, lenses 30 and 32, a reflecting mirror 33, and the like. The scanner unit 25 passes or reflects the laser light based on the image data emitted from the laser light source in the order of the polygon mirror 29, the lens 30, the reflecting mirror 33, and the lens 32, as indicated by a chain line, and will be described later. The surface of the photosensitive drum 31 of the cartridge 26 is irradiated with high-speed scanning.

(B) Process cartridge The process cartridge 26 is detachably attached to the main body casing 2 below the scanner unit 25. The process cartridge 26 includes a photosensitive drum 31 and a scorotron charger, a developing roller, a toner storage unit, and the like (not shown).

  The toner container is filled with a positively charged non-magnetic one-component polymerized toner as a developer, and the toner is carried on the developing roller as a thin layer having a constant thickness. On the other hand, the photosensitive drum 31 is rotatably disposed opposite to the developing roller, the drum body is grounded, and the surface thereof is formed by a positively charged photosensitive layer made of polycarbonate or the like. Yes.

  The surface of the photosensitive drum 31 is uniformly positively charged by the scorotron charger as the photosensitive drum 31 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 25. An electrostatic latent image based on the image data is formed, and thereafter, when the toner is opposed to the developing roller, the electrostatic charge toner formed on the developing roller and positively charged is formed on the surface of the photosensitive drum 31. The latent image, that is, the surface of the photosensitive drum 31 that is uniformly positively charged, is supplied to the portion exposed to the laser beam and the potential is lowered, and is selectively carried to be visualized. Thereby, reversal development is achieved.

  The transfer roller 34 is disposed below the photoconductive drum 31 so as to face the photoconductive drum 31 while being rotatably supported on the main body casing 2 side. In the transfer roller 34, a metal roller shaft is covered with a roller made of a conductive rubber material, and a predetermined transfer bias is applied to the photosensitive drum 31. Therefore, the visible image made of toner carried on the photosensitive drum 31 is transferred to the paper 3 while the paper 3 passes between the photosensitive drum 23 and the transfer roller 34. The sheet 3 on which the visible image is transferred is then conveyed to the fixing unit 27.

(C) Fixing Unit The fixing unit 27 includes a heating roller 42 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 43 that is disposed so as to press the heating roller 42. In the fixing device 27, the toner image is fixed on the paper 3 by heating the paper 3 carrying the toner image while being nipped and conveyed by the heating roller 42 and the pressure roller 43. Then, the heat-fixed paper 3 is conveyed to a paper discharge roller 44 provided on the upper portion of the main body casing 2, and is discharged onto the paper discharge tray 9 by the paper discharge roller 44.

(Electric configuration of laser printer)
Next, the electrical configuration of the laser printer 1 will be described. FIG. 3 is a block diagram showing an electrical configuration of the laser printer according to the first embodiment of the present invention.

  The laser printer 1 includes a control device 56 that includes a CPU 51, a ROM 52, a RAM 53, a control unit 54, a network interface 55, and the like. The ROM 52 stores various control programs for controlling the laser printer 1, various settings, initial values, and the like. The RAM 53 is used as a work area from which various control programs are read or as a storage area for temporarily storing print data.

  The CPU 51 controls each component of the laser printer 1 via the control unit 54 while storing the processing result in the RAM 53 according to the control program read from the ROM 52.

  An external device such as a computer 57 is connected to the network interface 55 and receives a print command, print data, and the like transmitted from the computer 57.

  The control unit 54 includes an ASIC, and includes a main motor 60, the image forming unit 5 described above, a pre-registration sensor 21, a post-registration sensor 22, a registration roller solenoid 61, a sheet feeding roller electromagnetic clutch 62, and sheet width detection. Each component of the laser printer 1 such as the sensor 64 is electrically connected.

  The main motor 60 is connected to the paper feed roller 13, the registration roller 14A, the multi-purpose side paper feed roller 15, the developing roller (not shown), the photosensitive drum 31, the heating roller 42, the paper discharge roller 44, etc. via a gear mechanism (not shown). Are connected and rotated while being synchronized.

(Operation when paper 3 is printed on the multi-purpose tray 14)
Next, the operation when the paper 3 on the multi-purpose tray 14 is printed will be described with reference to FIGS. 4, 5, and 6. 4 and 5 are timing charts showing the operation when printing on the paper on the multi-purpose tray according to the first embodiment of the present invention. FIG. 6 is a flowchart showing the flow of processing when a sheet on the multi-purpose tray is printed according to the first embodiment of the present invention.

  When the laser printer 1 receives a print command using the paper 3 on the multi-purpose tray 14 from the external computer 57, the process of the flowchart shown in FIG. 6 is started. When the print command is received, the CPU 11 receives print data transmitted from the computer 57 and starts an expansion process for expanding the print data on the RAM 53. At substantially the same time, the drive of the main motor 60 is started. When the print command is received, the paper width detection sensor 64 detects the guide width of the guide 65 that regulates the width of the paper 3 on the multi-purpose tray 14. The detected guide width is stored in the RAM 53 as the paper width of the paper 3. At least the A4 size paper width and the postcard size paper width are detected by the paper width detection sensor 64.

  When the development process for the print data for one page is completed, the electromagnetic clutch 62 for the feed roller is turned on, and the sheet 3 on the multi-purpose tray 14 is fed by the rotation of the multi-purpose side feed roller 15 (S101). ). As shown in FIG. 4, a driving force is supplied to the multipurpose side paper feed roller 15 to feed the paper 3. Next, it is determined whether or not the pre-registration sensor 21 has detected the sheet 3 (S102). When the pre-registration sensor 21 has not detected the paper 3 (S102: No), the printer waits for the paper 3 to be carried.

  When the pre-registration sensor 21 detects the sheet 3 (S102: Yes), the registration roller solenoid 61 is turned on before the sheet 3 reaches the registration rollers 14A and 14B (S103). When the registration roller solenoid 61 is turned on, the rotation of the registration rollers 14A and 14B is stopped. At this time, as shown in FIG. 4, since the driving force continues to be supplied to the multi-purpose sheet feeding roller 15 that feeds the sheet 3, the sheet 3 is conveyed to the stopped registration rollers 14A and 14B. The leading edge of the paper 3 hits. The skew of the sheet 3 is corrected by the front end of the sheet 3 being abutted against the registration rollers 14A and 14B.

  It is determined whether or not a predetermined time T1 from when the registration roller solenoid 61 is turned on in S103 until the skew of the sheet 3 is corrected has passed (S104). When the predetermined time T1 has not elapsed (S104: No), the paper 3 is fed by the multi-purpose feed roller 15 with the registration roller solenoid 61 turned on. When the predetermined time T1 has elapsed (S104: Yes), the registration roller solenoid 61 is turned off (S105). When the registration roller solenoid 61 is turned off, rotation of the registration rollers 14A and 14B is started. Then, the sheet 3 whose skew has been corrected is conveyed toward the image forming unit 5 by the rotation of the registration rollers 14A and 14B.

  Next, it is determined whether or not the paper width detected by the paper width detection sensor 64 is a postcard size (S106). If the paper width detected by the paper width detection sensor 64 is, for example, A4 size and not the postcard size (S106: No), the sheet feeding roller electromagnetic clutch 62 is turned off (S109). When the sheet feeding roller electromagnetic clutch 62 is turned off, the power transmission to the multi-purpose sheet feeding roller 15 is cut off, and only the conveying force of the registration rollers 14A and 14B until the sheet 3 reaches the photosensitive drum 31. Is conveyed by. For example, when the paper width is not the postcard size but the A4 size, even if the paper 3 is transported only by the transport force of the registration rollers 14A and 14B, the possibility of skewing is extremely low. Therefore, even when the paper feed roller electromagnetic clutch 62 is turned off at the timing when the paper 3 starts to be transported by the registration rollers 14A and 14B, the paper 3 can be transported appropriately. The CPU 51 and S106 of this embodiment are an example of the paper width determination unit of the present invention.

  If the paper width detected by the paper width detection sensor 64 is a postcard size (S106: Yes), it is determined whether or not the leading edge of the paper 3 has passed between the photosensitive drum 31 and the transfer roller 34 (S106: Yes). S107). Whether or not the leading edge of the sheet 3 has passed between the photosensitive drum 31 and the transfer roller 34 is determined by whether or not the sheet 3 has passed the post-registration sensor 22 and a predetermined time T2 has elapsed. The predetermined time T2 is a time required from the timing when the post-registration sensor 22 detects the leading edge of the paper 3 to the time when the leading edge of the paper 3 passes between the photosensitive drum 31 and the transfer roller 34.

When it is determined that the leading edge of the sheet 3 does not pass between the photosensitive drum 31 and the transfer roller 34 (S107: No), the trailing edge of the sheet 3 is positioned immediately before the multi-purpose-side sheet feeding roller 15. It is determined whether or not it has been reached (S108). The position immediately before the multi-purpose-side paper feed roller 15 is a position where the multi-purpose-side paper feed roller 15 can carry the paper 3 and the next paper 3 without double feeding. If it is determined that the trailing edge of the sheet 3 has not reached the position immediately before the multi-purpose sheet feeding roller 15 (S108: No), the process returns to S107. The processes of S107 and S108 are performed until the leading edge of the sheet 3 passes between the photosensitive drum 31 and the transfer roller 34, or until the trailing edge of the sheet 3 reaches the position immediately before the multi-purpose-side sheet feeding roller 15. Repeated. While the processes of S107 and S108 are repeated, as shown in FIG. 4, the driving force is continuously supplied to the multi-purpose sheet feeding roller 15, and the sheet 3 is conveyed by the registration rollers 14A and 14B. . That is, the sheet 3 is conveyed by the multi-purpose-side sheet feeding roller 15 and the two rollers having the conveying force of the registration rollers 14A and 14B. Accordingly, it is possible to prevent the sheet 3 having a postcard size sheet width from being conveyed only by the conveying force of the registration rollers 14A and 14B and the sheet 3 being skewed.

  When it is determined that the leading edge of the sheet 3 has passed between the photosensitive drum 31 and the transfer roller 34 (S107: Yes), the sheet feeding roller electromagnetic clutch 62 is turned off (S109). When the feed roller electromagnetic clutch 62 is turned off, the power transmission to the multi-purpose feed roller 15 is cut off. When the leading edge of the sheet 3 passes between the photosensitive drum 31 and the transfer roller 34, the sheet 3 is conveyed by the photosensitive drum 31 having a conveying force. Since the sheet 3 is conveyed by the two rollers having the conveying force of the photosensitive drum 31 and the registration rollers 14A and 14B even if the conveying force of the multipurpose-side sheet feeding roller 15 is lost, the sheet 3 is skewed. Can be suppressed. At this time, as shown in FIG. 4, when a predetermined time T2 has elapsed since the leading edge of the sheet 3 was detected by the post-registration sensor 22, the conveyance of the sheet 3 by the photosensitive drum 31 is started. Simultaneously with this start, a visible image is transferred to the paper 3.

  When it is determined that the leading edge of the sheet 3 has not passed between the photosensitive drum 31 and the transfer roller 34 (S107: No), and the trailing edge of the sheet 3 is immediately before the multi-purpose-side sheet feeding roller 15. When it is determined that the position has been reached (S108: Yes), the sheet feeding roller electromagnetic clutch 62 is turned off (S109). That is, the sheet 3 is conveyed only by the conveying force of the registration rollers 14A and 14B until the leading edge of the sheet 3 passes between the photosensitive drum 31 and the transfer roller 34. As shown in FIG. 5, even if the leading end of the sheet 3 does not pass between the photosensitive drum 31 and the transfer roller 34, the sheet length of the sheet in the transport direction is changed from the multipurpose-side sheet feeding roller 15 to the registration roller 14A. , 14B is shorter than the paper transport distance, and when the trailing edge of the paper 3 reaches the position immediately before the multi-purpose side paper feeding roller 15, the paper 3 is used for the paper feeding roller so as not to double-feed the next paper 3. The electromagnetic clutch 62 is turned off. Accordingly, the sheet 3 is conveyed only by the conveying force of the registration rollers 14A and 14B until the conveying force of the multipurpose-side sheet feeding roller 15 is lost and the leading edge of the sheet 3 passes between the photosensitive drum 31 and the transfer roller 34. Is done. The determination as to whether the trailing edge of the sheet 3 has reached the position immediately before the multi-purpose-side feed roller 15 is performed by, for example, determining the sheet length information included in the print data transmitted from the computer 57 and the multi-purpose-side feed roller 15. This is carried out using the sheet conveyance distance calculated from the driving time.

  When the distance from the multipurpose feed roller 15 to the photosensitive drum 31 is longer than the paper length of the paper 3 on the paper transport path, the trailing edge of the paper 3 is immediately before the multipurpose feed roller 15. Until the position is reached, the paper 3 can be transported by two rollers having the transporting force of the multi-purpose side paper feed roller 15 and the registration rollers 14A and 14B.

  The sheet 3 to which the visible image is transferred is then conveyed to the fixing unit 27 and then discharged onto the sheet discharge tray 9. When the printing of the sheet 3 is completed, this flowchart ends.

[Second Embodiment]
A second embodiment will be described with reference to FIGS. 7, 8, and 9. FIG. 7 is a block diagram showing an electrical configuration of a laser printer according to the second embodiment of the present invention. FIG. 8 is a timing chart showing an operation when a sheet on a multi-purpose tray according to the second embodiment of the present invention is printed. FIG. 9 is a flowchart showing the flow of processing when a sheet on a multi-purpose tray is printed according to the second embodiment of the present invention.

  The second embodiment is common to the entire internal configuration of the laser printer shown in FIG. 1 in the first embodiment. 7 to 9, the same configurations and processes as those in the first embodiment are used for the reference numerals used in the first embodiment. The description of the configuration and processing common to the first embodiment is omitted. In the second embodiment, a mechanism for transmitting a driving force to the multipurpose-side sheet feeding roller 15 is used instead of the sheet feeding roller electromagnetic clutch 62 instead of the sheet feeding roller electromagnetic clutch 62. .

  In the second embodiment, as shown in FIG. 7, the paper feed roller solenoid 63 and the control unit 54 are electrically connected. The feed roller solenoid 63 is provided as a mechanism for transmitting a driving force between the main motor 60 and the multi-purpose feed roller 15 and is turned on, and at the same time from the main motor 60 to the multi-purpose feed roller 15. The driving force is supplied, and the paper 3 and the multi-purpose-side paper supply roller 15 come into contact with each other. The driving force is supplied to the multi-purpose sheet feed roller 15 until a predetermined time T3 has elapsed until the leading edge of the sheet 3 reaches the registration rollers 14A and 14B from the multi-purpose sheet feed roller 15. When the predetermined time T3 elapses, the driving force supplied to the multipurpose paper feed roller 15 is cut off, and the multipurpose paper feed roller 15 is separated from the paper 3. Note that the paper feed roller solenoid 63 is turned off until the predetermined time T3 elapses. Even when the sheet feed roller solenoid 63 is turned off, the driving force is supplied to the multipurpose sheet feed roller 15 until the predetermined time T3 elapses. The predetermined time T4 from when the paper feed roller solenoid 63 is turned on to when it is turned off is set to 100 ms, for example.

  When the laser printer 1 receives a print command using the paper 3 on the multi-purpose tray 14 from the external computer 57, the process of the flowchart shown in FIG. 9 is started. When the print command is received, the CPU 11 receives print data transmitted from the computer 57 and starts an expansion process for expanding the print data on the RAM 53. At substantially the same time, the drive of the main motor 60 is started.

  When the development process for one page of print data is completed, the feed roller solenoid 63 is turned on (S201). At the same time as the sheet feeding roller solenoid 63 is turned on, the driving force is supplied to the multi-purpose side sheet feeding roller 15 and the sheet 3 on the multi-purpose tray 14 is fed. Next, it is determined whether or not a predetermined time T4 has elapsed since the feed roller solenoid 63 is turned on (S202).

  When it is determined that the predetermined time T4 has not elapsed since the feed roller solenoid 63 is turned on (S202: No), the state where the feed roller solenoid 63 is turned on is maintained, and the process of S202 is performed. Is repeated. When it is determined that the predetermined time T4 has elapsed since the feed roller solenoid 63 is turned on (S202: Yes), the feed roller solenoid 63 is turned off (S203). As shown in FIG. 9, even when the sheet feed roller solenoid 63 is turned off, the driving force is continuously supplied to the multipurpose sheet feed roller 15 until the sheet 3 is conveyed by the registration rollers 14A and 14B.

  Next, when the leading edge of the sheet 3 reaches the pre-registration sensor 21, the pre-registration sensor 21 is turned on (S102: Yes), and the registration roller solenoid 61 is turned on (S103). The leading edge of the paper 3 hits the stopped registration rollers 14A and 14B, and the skew of the paper 3 is corrected. When a predetermined time T1 elapses from when the registration roller solenoid 61 is turned on until the skew of the sheet 3 is corrected (S104: Yes), the registration roller solenoid 61 is turned off (S105). At the same time as the registration roller solenoid 61 is turned off, the sheet 3 starts to be conveyed by the registration rollers 14A and 14B.

  Next, it is determined whether or not the paper width detected by the paper width detection sensor 64 is a postcard size (S106). When the paper width detected by the paper width detection sensor 64 is a postcard size (S106: Yes), the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once has elapsed. It is determined whether or not (S204). The diameter of the multi-purpose side feed roller 15 and the registration from the multi-purpose side feed roller 15 so that the leading edge of the paper 3 reaches the registration rollers 14A and 14B by one rotation of the multi-purpose side feed roller 15 A distance on the paper conveyance path to the rollers 14A and 14B is set.

  When it is determined that the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S204: No), the process of S204 is repeated. When it is determined that the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S204: Yes), the paper feed roller solenoid 63 is turned on (S205). ). As shown in FIG. 9, after the sheet 3 is conveyed by the registration rollers 14 </ b> A and 14 </ b> B, the driving force to the multi-purpose side feed roller 15 is cut off, and the time for one cycle of the multi-purpose side feed roller 15 elapses. To do. When a time corresponding to one cycle of the multi-purpose sheet feeding roller 15 has elapsed, the sheet feeding roller solenoid 63 is turned on. At the same time as the paper feed roller solenoid 63 is turned on, a driving force is supplied to the multipurpose side paper feed roller 15.

  Next, it is determined whether or not a predetermined time T4 has elapsed since the feed roller solenoid 63 is turned on (S206). When it is determined that the predetermined time T4 has not elapsed since the feed roller solenoid 63 is turned on (S206: No), the state where the feed roller solenoid 63 is turned on is maintained, and the process of S206 is performed. Is repeated. When it is determined that the predetermined time T4 has elapsed since the feed roller solenoid 63 is turned on (S206: Yes), the feed roller solenoid 63 is turned off (S207). As shown in FIG. 9, in order to convey one sheet 3, the sheet feed roller solenoid 63 is turned on twice, while the sheet 3 is being conveyed by the multipurpose sheet feed roller 15. 3 reaches the photosensitive drum 31. At this time, the sheet 3 is conveyed by the multi-purpose-side sheet feeding roller 15, the registration rollers 14 </ b> A and 14 </ b> B, and the photosensitive drum 31. Even if the driving force supplied to the multi-purpose sheet feeding roller 15 is interrupted, the sheet 3 is conveyed by the registration rollers 14A and 14B and the photosensitive drum 31, so that the skew of the sheet 3 can be suppressed. .

[Third Embodiment]
A third embodiment will be described with reference to FIGS. 10 and 11. FIG. 10 is a timing chart showing an operation when a sheet on a multi-purpose tray is printed according to the third embodiment of the present invention. FIG. 11 is a flowchart showing the flow of processing when a sheet on a multi-purpose tray is printed according to the third embodiment of the present invention.

  The third embodiment is common to the entire internal configuration of the laser printer shown in FIG. 1 in the first embodiment and the electrical configuration shown in FIG. 7 in the second embodiment. In FIGS. 10 and 11, the same configurations and processes as those in the first embodiment or the second embodiment are used in the first embodiment or the second embodiment. Is used. The description of the configuration and processing common to the first embodiment or the second embodiment is omitted. In the third embodiment, in the second embodiment, the skew of the sheet 3 is corrected by stopping the rotation of the registration rollers 14A and 14B, and the registration roller solenoid 61 is turned off. The operation of turning on the roller solenoid 61 is different from that of the second embodiment.

  As shown in FIG. 11, in S105, the skew of the sheet 3 is corrected, the registration roller solenoid 61 is turned off, and the sheet width detected by the sheet width detection sensor 64 is determined to be the postcard size. In the case (S106: Yes), it is determined whether or not a predetermined time T5 necessary for the leading edge of the sheet 3 to be sandwiched between the registration rollers 14A and 14B has passed (S301). The sheet 3 is conveyed until a predetermined time T5 necessary for the leading edge of the sheet 3 to be held between the registration rollers 14A and 14B has passed (S301: No).

  When it is determined that the predetermined time T5 necessary for the leading edge of the sheet 3 to be held between the registration rollers 14A and 14B has elapsed (S301: Yes), the registration roller solenoid 61 is turned on (S302). When the registration roller solenoid 61 is turned on, the conveyance of the sheet is temporarily stopped while the sheet 3 is held between the registration rollers 14A and 14B. As shown in FIG. 11, at the same time as the driving force supplied to the multi-purpose-side paper supply roller 15 is cut off, the registration roller solenoid 61 is turned on. Accordingly, when the driving force supplied to the multi-purpose-side paper supply roller 15 is interrupted, the paper 3 is not conveyed only by the registration rollers 14A and 14B. Therefore, even in the configuration using the registration roller solenoid 61, the paper is not conveyed. 3 skewing can be suppressed.

  It is determined whether or not a time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S303). The process of S303 is repeated until the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S303: No). When it is determined that the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S303: Yes), the paper feed roller solenoid 63 is turned on (S304). ). When the paper feed roller solenoid 63 is turned on, the driving force is supplied to the multi-purpose side paper feed roller 15 and the conveyance of the paper 3 is resumed. At this time, even if the conveyance of the sheet 3 by the multipurpose-side sheet feeding roller 15 is resumed, the rotation of the registration rollers 14A and 14B is stopped, so that the sheet 3 is held between the registration rollers 14A and 14B. .

  Next, it is determined whether or not a predetermined time T6 has elapsed until the sheet 3 is conveyed again (S305). This is generally defined as the time required for solenoid delay or gear connection. If it is determined that the predetermined time T6 has passed (S305: Yes), the registration roller solenoid 61 is turned off (S306). The process of S305 is repeated until the predetermined time T6 elapses (S305: No).

  Next, it is determined whether or not a predetermined time T7 has elapsed since the feed roller solenoid 63 is turned on (S307). The process of S307 is repeated until a predetermined time T7 elapses after the feed roller solenoid 63 is turned on (S307: No). If it is determined that the predetermined time T7 has elapsed since the feed roller solenoid 63 is turned on (S307: Yes), the feed roller solenoid 63 is turned off (S308).

[Fourth Embodiment]
A fourth embodiment will be described with reference to FIGS. 12 and 13. FIG. 12 is a timing chart showing an operation when a sheet on a multi-purpose tray is printed according to the fourth embodiment of the present invention. FIG. 13 is a flowchart showing the flow of processing when a sheet on a multi-purpose tray is printed according to the fourth embodiment of the present invention.

  The fourth embodiment is common to the entire internal configuration of the laser printer shown in FIG. 1 in the first embodiment and the electrical configuration shown in FIG. 7 in the second embodiment. In FIGS. 12 and 13, the same configurations and processes as those in the first embodiment, the second embodiment, or the third embodiment are used in the first embodiment and the second embodiment. Or the code | symbol used in 3rd Embodiment is used. The description of the configuration and processing common to the first embodiment, the second embodiment, or the third embodiment is omitted. In the fourth embodiment, the processes from S104 to S303 in the third embodiment are different. Specifically, in the fourth embodiment, after the registration roller solenoid 61 is once turned off in S105 in the third embodiment, the processing for turning on the registration roller solenoid 61 in S302 is not performed, and in S103. The third embodiment is different from the third embodiment in that when the registration roller solenoid 61 is turned on, the registration roller solenoid 61 is not turned off until S306.

  As shown in FIG. 13, the registration roller solenoid 61 is turned on in S103, and the rotation of the registration rollers 14A and 14B is stopped to correct the skew of the sheet 3. When the registration roller solenoid 61 is turned on in S103, it is determined whether or not the paper width detected by the paper width detection sensor 64 is a postcard size (S401). When it is determined that the paper width detected by the paper width detection sensor 64 is not the postcard size (S401: No), the processing of this flowchart ends, and the paper 3 is conveyed to the image forming unit 5 and printing is performed.

  If it is determined that the paper width detected by the paper width detection sensor 64 is the postcard size (S401: Yes), the paper width is one cycle required for the paper feeding operation performed by the multipurpose side paper feeding roller 15 rotating once. It is determined whether or not the time elapses (S402). The process of S402 is repeated until the time corresponding to one cycle for the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S402: No). If it is determined that the time corresponding to one cycle of the paper feeding operation performed by rotating the multi-purpose side paper feeding roller 15 once (S402: Yes), the paper feed roller solenoid 63 is turned on (S304). ).

  As shown in FIG. 13, after the registration roller solenoid 61 is turned on and the rotation of the registration rollers 14A and 14B is stopped, the sheet 3 is registered until the driving force supplied to the multi-purpose side paper supply roller 15 is cut off. The paper 3 is bent against the rollers 14A and 14B. When the driving force supplied to the multi-purpose-side paper supply roller 15 is interrupted, the deflection of the paper 3 is restored and the force with which the paper 3 is abutted against the registration rollers 14A and 14B is weakened. At the timing when the second feeding roller solenoid 63 is turned on, the sheet 3 is again abutted against the registration rollers 14A and 14B. At this time, it is determined whether or not a time necessary for correcting the skew of the sheet 3 has passed (S305). The process of S305 is repeated until the time necessary for correcting the skew of the sheet 3 has elapsed (S305: No). When it is determined that the time necessary for correcting the skew of the sheet 3 has elapsed (S305: Yes), the rotation of the registration rollers 14A and 14B is started, and the sheet 3 is conveyed to the image forming unit 5. A printing operation is performed.

[Modification]
The present invention is not limited to this embodiment, and various modifications can be made without departing from the spirit of the present invention. An example of the modification will be described below.

  In this embodiment, the case where the sheet 3 on the multi-purpose tray is printed is described for the printing of the image forming apparatus according to the present invention. However, the printing of the image forming apparatus according to the present invention is placed on the paper feed tray 11. This can also be applied to the case where the printed paper 3 is printed. The electromagnetic clutch 62 for the paper feed roller is provided as a clutch mechanism between the main motor 60 and the paper feed roller 13, and when it is turned on, power is transmitted from the main motor 60 to the paper feed roller 13 and is turned off. Sometimes the power transmission is cut off. As a clutch mechanism, a paper feed roller solenoid 63 may be used instead of the paper feed roller electromagnetic clutch 62.

  In the present embodiment, the case where the cross section of the paper feed roller 13 and the multipurpose paper feed roller 15 according to the present invention is circular has been described. However, the paper feed roller 13 and the multipurpose paper feed roller are described. 15 may be a D-shaped paper feed roller 13 and a multipurpose paper feed roller 15.

  In the present embodiment, the timing for interrupting the driving force supplied to the multi-purpose-side paper feed roller 15 is controlled by determining whether or not the paper width is a postcard size, but it is less than the paper width of the postcard size. Whether or not the driving force supplied to the multi-purpose sheet feeding roller 15 is interrupted may be controlled by determining whether or not the multi-purpose sheet feeding roller 15 is not.

  In this embodiment, the case where the postcard size paper width 3 is printed in the laser printer 1 capable of printing an A4 size paper width has been described, but B5 in the laser printer 1 capable of printing an A3 size paper width. The present invention can also be applied to a case where a sheet 3 having a sheet width of a size is printed. The postcard size may be an envelope size.

  In this embodiment, the paper width is detected by using the paper width detection sensor 64, but may be performed by using paper width information included in the print data transmitted from the computer 57. In addition, information on the sheet width set from an operation panel (not shown) of the laser printer 1 may be used.

DESCRIPTION OF SYMBOLS 1 Laser printer 5 Image formation part 13 Paper feed roller 15 Multipurpose side paper feed roller 14A Registration roller (drive side)
14B Registration roller (driven side)
21 Sensor before registration 22 Sensor after registration 51 CPU
52 ROM
53 RAM
54 Controller 55 Network I / F
56 Control Device 57 Computer 60 Main Motor 61 Solenoid for Registration Roller 62 Electromagnetic Clutch for Paper Feeding Roller 64 Paper Width Detection Sensor

Claims (8)

A printing unit that prints an image on a sheet, a sheet that has a predetermined first width in a direction perpendicular to the sheet conveyance direction, and a second sheet that is narrower than the first width are provided in the printing unit. In an image forming apparatus provided with a transport mechanism for transporting,
A first roller for conveying paper;
A pair of registration rollers for correcting skew of the paper conveyed by the first roller;
When the sheet width of the sheet to be conveyed is the first width, after the skew feeding of the sheet is corrected by the registration roller pair, the conveying force transmitted to the sheet by the first roller is cut off, and the sheet is not registered. When the sheet width of the sheet conveyed to the printing unit by the roller pair is the second width, the conveyance force to the sheet by the first roller even after the skew of the sheet is corrected by the registration roller pair. And a control unit that controls the transport mechanism so that the sheet is transported to the printing unit by the first roller and the registration roller pair. The image forming apparatus according to claim 1.
A second roller capable of conveying the sheet conveyed by the registration roller pair;
When the paper length in the transport direction of the transported paper is longer than the first paper transport distance from the first roller to the second roller, the control unit waits until the leading edge of the paper reaches the second roller. An image forming apparatus, wherein the conveyance mechanism is controlled so that a sheet is conveyed by the first roller and then a conveyance force transmitted to the sheet by the first roller is interrupted. The image forming apparatus according to claim 2.
When the paper length in the transport direction of the transported paper is shorter than the first paper transport distance, the control unit is configured to perform the first control immediately before the rear end of the paper passes through the contact position with the first roller. An image forming apparatus, wherein the conveyance mechanism is controlled so that a conveyance force transmitted to the sheet by one roller is interrupted. The image forming apparatus according to claim 1, wherein:
A paper width determining unit that determines whether the paper width of the conveyed paper is the first width or the second width;
The paper width determination unit includes a paper width sensor that detects the paper width, and the paper width of the paper conveyed by the output of the paper width sensor is the first width or the second width. An image forming apparatus that determines whether or not there is an image. The image forming apparatus according to any one of claims 1 to 4, wherein:
The first roller has a sheet conveyance distance by one conveyance operation of the first roller that is larger than a second sheet conveyance distance from the first roller to the registration roller pair,
When the sheet width of the sheet to be transported is the first width, the control unit stops the transport operation after the transport operation is performed once, and the sheet width of the sheet to be transported is the second width. In this case, the image forming apparatus controls the transport mechanism so that the transport operation is stopped after the transport operation is performed at least twice. The image forming apparatus according to any one of claims 1 to 4, wherein:
The first roller has a sheet conveyance distance by one conveyance operation of the first roller that is larger than a second sheet conveyance distance from the first roller to the registration roller pair, and one conveyance operation. The first roller and the paper are in contact with each other, and when the transport operation is finished, the first roller and the paper are separated,
When the sheet width of the sheet to be transported is the first width, the control unit stops the transport operation after the transport operation is performed once, and the sheet width of the sheet to be transported is the second width. In this case, the image forming apparatus controls the transport mechanism so that the transport operation is stopped after the transport operation is performed at least twice. The image forming apparatus according to claim 5 or 6, wherein:
The control unit stops rotation of the registration roller pair from when the registration roller pair pinches the leading edge of the sheet until the conveying force transmitted to the sheet by the first roller is interrupted. Forming equipment. The image forming apparatus according to any one of claims 1 to 7,
The registration roller pair includes a driving roller and a driven roller,
At least one of the driving roller and the driven roller is rotatably supported by two bearings, and is pressed against the other roller via the two bearings by the action of a spring, and one of the two bearings is disposed. An image forming apparatus, wherein a distance from a position where the other bearing is disposed to a position where the other bearing is disposed is greater than the second width.

Images