JP2014065553A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an occurrence of a fault during paper conveyance in the case of conveying stiff paper in an image forming apparatus with an S-shaped bent path provided in a paper conveyance part.SOLUTION: In an image forming apparatus in which conveying rollers 231 to 233, a loop roller 234, and a resist roller 235 are sequentially arranged from an upstream side of a conveyance path in a conveyance part for conveying paper toward a transfer part for transferring a toner image on the paper, and an S-shaped bent path 236 is provided, a discrimination part 106 discriminates whether paper to be conveyed is a prescribed first paper kind or a prescribed second paper kind, when discriminated to be the first paper kind, the conveying rollers 231 to 233 are separated from the paper before the paper is caused to rush to the resist roller 235, and when discriminated to be the second paper kind, the conveying rollers 231 to 233 are separated from the paper after the paper is nipped by the resist roller 235.

Description

  The present invention relates to an image forming apparatus for transferring a toner image formed on an image carrier such as a photosensitive member to a sheet as a transfer material, and in particular, an image in which a path bent in an S-shape is provided in a sheet conveyance unit. The present invention relates to a forming apparatus.

  The charged photoconductor is exposed based on image data to form an electrostatic latent image, and a toner image is formed by attaching toner to the photoconductor, and the toner image is transferred to a sheet as a transfer material. Accordingly, image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines that form images have become widespread.

  In such an image forming apparatus, in general, a registration roller is arranged immediately upstream of the transfer position and a plurality of conveyance rollers is arranged upstream of the registration roller in a conveyance unit that conveys the sheet to the transfer position of the toner image. Has been. In the conveyance unit, after the sheet is conveyed to the registration roller by the conveyance roller, the sheet is sent to the transfer position by the registration roller at a timing at which the toner image can be transferred to the sheet.

  In general, among the plurality of conveyance rollers, the conveyance roller immediately upstream of the registration roller is a loop roller that continuously conveys the sheet after the sheet arrives at the registration roller and bends the sheet in a loop (forms a registration loop). As a role. Even when the sheet is conveyed while being inclined, by forming such a registration loop, it is possible to correct the inclination by changing the direction of the sheet so that the entire front end of the sheet contacts the registration roller uniformly.

  Conventionally, in an image forming apparatus provided with such a conveyance unit, immediately before the sheet enters the registration roller, all the conveyance rollers that nip the sheet upstream of the loop roller are separated from the sheet. . This is because when the registration loop is formed to change the direction of the paper, the direction of the paper is easier to change if the number of rollers niping the paper is smaller.

  Note that the following [1] and [2] have been disclosed as techniques based on the premise that the loop roller and the conveyance roller on the upstream side of the registration roller are separated from the sheet.

  [1] By separating the loop roller from the paper a predetermined time after the registration roller starts rotating, even if the amount of bending is not uniform in the width direction of the paper when the registration loop is formed, The non-uniformity is eliminated, and wrinkles are not generated on the sheet fed by the registration rollers (see, for example, Patent Document 1).

  [2] A swing mechanism for swinging the registration roller in the width direction of the sheet is provided. In addition, a reference guide as a paper positioning member is provided immediately upstream of the registration roller in parallel with the paper transport direction, and a skew roller for transporting the paper so as to approach the reference guide is provided. Then, after correcting the inclination of the sheet by abutting the side edge of the sheet with the reference guide by the skew roller, when the sheet is nipped by the registration roller, the skew roller is separated from the sheet and the registration roller is swung. As a result, the position in the width direction of the sheet is corrected (see, for example, Patent Document 2).

JP-A-11-165914 JP-A-11-189355

  By the way, when designing the image forming apparatus, there may be a case where a path bent in an S shape is provided in the transport path of the transport unit. As an example of such a case, it is desired that an existing large-capacity paper feeding unit can be installed as an option in the image forming apparatus. However, because of the height of the position at which paper is fed from the paper feeding unit, paper feeding There is a case in which the used paper has to be conveyed through a path bent in an S shape within the image forming apparatus.

  FIG. 7 shows an example of such an S-shaped bending path. The right side of FIG. 7 is the upstream side of the transport path, and the transport roller 301, the transport roller 302, the transport roller 303, the loop roller 304, and the registration roller 305 are sequentially arranged from the upstream side to the downstream side. FIG. 7 shows a state in which the sheet S being conveyed is in a position immediately before entering the registration roller 305 and is nipped by all of the conveyance rollers 301 to 303 and the loop roller 304. An S-shaped bent path 306 is formed between the transport roller 301 and the transport roller 302. The bent path 306 has a downward convex curve 307, and an upper guide plate 308 is provided on the upper side of the downward convex curve 307.

  However, in such an image forming apparatus provided with the S-shaped bending path 306, as shown in FIG. 7, the conveying roller on the upstream side of the loop roller 304 immediately before the sheet enters the registration roller 305 as in the prior art. When all of 301-303 are separated from the sheet S, the upper guide plate 308 and the sheet S come into contact with each other when a so-called stiff sheet such as a thick sheet, a sheet having high rigidity, or a sheet having a high frictional resistance value is conveyed. As a result, the resistance during conveyance increases, and the sheet S is conveyed only by the loop roller 304. Therefore, troubles may occur in the conveyance of the sheet S due to sudden load fluctuations or insufficient conveyance force.

  In Patent Documents 1 and 2 mentioned above, there is no mention of the timing at which the transport roller upstream of the loop roller is separated from the paper when such a path bent in an S shape is provided in the transport unit. .

  In view of the above points, the present invention provides an image forming apparatus in which a path bent in an S-shape is provided in a paper transport unit, such as thick paper, high rigidity paper, high friction resistance paper, and the like. An object is to prevent a conveyance failure when conveying a sheet.

  In order to solve the above problems and achieve the object of the present invention, an image forming apparatus of the present invention includes an image forming unit that forms a toner image on an image carrier, a transfer unit that transfers the toner image to a sheet, and a transfer unit. A conveyance section having a conveyance path bent in an S-shape for conveying a sheet toward the paper, a conveyance roller, a loop roller, a registration roller arranged in order from the upstream side along the conveyance path, and a sheet conveyed by the conveyance section A determination unit that determines whether the first paper type is a predetermined first paper type or a predetermined second paper type, and if the determination unit determines that the paper is the first paper type, If the conveying roller is separated from the sheet before the toner enters, and the determination unit determines that the sheet is the second sheet type, the conveying roller is separated from the sheet after the sheet is nipped by the registration roller. A control unit for controlling.

  According to the image forming apparatus configured as described above, the timing for separating the transport roller upstream of the registration rollers from the sheet is determined according to the determination result of the sheet type. As a result, the resistance of the sheet on the conveyance path bent in an S shape increases during the conveyance of the sheet, and even if a sudden load fluctuation or insufficient sheet conveyance force occurs, the sheet can be reliably conveyed. it can.

1 is a diagram illustrating a configuration of an image forming unit, an intermediate transfer belt, a secondary transfer unit, a fixing unit, and the like of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a conveyance unit of the image forming apparatus according to the first exemplary embodiment of the present invention. 1 is a block diagram illustrating a configuration of a control system of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a diagram illustrating a separation timing of a conveyance roller during thick card conveyance in the image forming apparatus according to the first exemplary embodiment of the present invention. It is a flowchart which shows the control processing of the conveyance part in the 2nd Embodiment of this invention. FIG. 10 is a diagram illustrating a separation timing of a conveyance roller during thick card conveyance in an image forming apparatus according to a second embodiment of the present invention. It is a figure which shows an example of a S-shaped bending path | route.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 shows configurations of an image forming unit, an intermediate transfer belt, a secondary transfer unit, a fixing unit, and the like of an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and tandem format in which toners of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) are superimposed. The color image forming apparatus. The image forming apparatus 1 includes a document transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50, a secondary transfer unit 70, and a fixing unit 80.

  The document transport unit 10 includes a document feeder 11 on which a document is set and a plurality of rollers 12. The documents G set on the document feeder 11 of the document transport unit 10 are transported one by one to the reading position of the image reading unit 30 by the plurality of rollers 12. The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 13 and generates an image signal.

  The paper storage unit 20 is disposed in the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size of the paper S. The sheet S is fed by the sheet feeding unit 21 and sent to the transport unit 23, and is transported by the transport unit 23 to the secondary transfer unit 70 that is a transfer position. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP sheet is sent to the transfer position. Further, the image forming apparatus 1 can be optionally equipped with a large-capacity paper feed unit 2 (only the end portion is shown in the figure), and the paper fed from the paper feed unit 2 is also available. It is sent to the transport unit 23. Due to the height of the position where the paper is fed from the paper feeding unit 2, the paper conveyance path from the paper feeding unit 2 in the conveyance unit 23 is provided with a bent path 236 which is a path bent in an S shape. It has been.

  An image forming unit 40 and an intermediate transfer belt 50 are disposed between the image reading unit 30 and the paper storage unit 20. The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk). .

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, only the first image forming unit 40Y will be described here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 arranged around the photoconductor 41, an exposure unit 43, a developing unit 44, and a cleaning unit 45. The photoreceptor 41 is rotated counterclockwise by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The exposure unit 43 performs exposure scanning on the surface of the photoconductor 41 based on the image data read from the document G, and forms an electrostatic latent image on the photoconductor 41.

  The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41 that is an image carrier. As a result, a yellow toner image is formed on the surface of the photoreceptor 41. The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.

  The toner adhering to the photoreceptor 41 is transferred to an intermediate transfer belt 50 showing an example of an image carrier. The cleaning unit 45 removes toner remaining on the surface of the photoreceptor 41 after being transferred to the intermediate transfer belt 50.

  The intermediate transfer belt 50 is formed in an endless shape, and is rotated clockwise by a drive motor (not shown) in a direction opposite to the rotation direction of the photoconductor 41. A primary transfer portion 51 is provided at a position on the intermediate transfer belt 50 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 51 transfers the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50 by applying a polarity opposite to that of the toner to the intermediate transfer belt 50.

  As the intermediate transfer belt 50 rotates, the toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 50. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 50 to form a color image.

  A secondary transfer unit 70 is disposed near the intermediate transfer belt 50 and downstream of the conveyance unit 23. The secondary transfer unit 70 is composed of opposed rollers, and presses the sheet S sent by the transport unit 23 to the intermediate transfer belt 50 side. The secondary transfer unit 70 transfers the color image formed on the intermediate transfer belt 50 onto the paper S sent by the transport unit 23. The cleaning unit 52 removes toner remaining on the surface of the intermediate transfer belt 50 after being transferred to the paper S. A fixing unit 80 is provided on the paper transfer side of the secondary transfer unit 70. The fixing unit 80 pressurizes and heat-fixes the toner image transferred to the paper S.

  A switching gate 24 is disposed downstream of the fixing unit 80. The switching gate 24 switches the transport path of the paper S that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper S straight when performing face-up paper discharge in single-sided image formation. As a result, the paper S is discharged by the pair of paper discharge rollers 25. The switching gate 24 guides the paper S downward when face-down paper discharge and double-sided image formation in single-sided image formation.

When face-down paper discharge is performed, the paper S is guided downward by the switching gate 24, and then the front and back sides are reversed by the paper reverse conveyance unit 26 and conveyed upward. As a result, the paper S is discharged by the pair of paper discharge rollers 25.
When double-sided image formation is performed, the sheet S is guided downward by the switching gate 24, the front and back sides are reversed by the sheet reversing conveyance unit 26, and sent again to the transfer position by the refeed path 27.

  Further, a post-processing device that folds the paper S or performs stapling processing or the like on the paper S may be disposed downstream of the pair of paper discharge rollers 25.

  FIG. 2 shows the configuration of the part of the transport path for transporting the paper fed from the paper feed unit 2 in the transport unit 23 shown in FIG. The right side of FIG. 2 is the upstream side of the transport path, and transport rollers 231, transport rollers 232, transport rollers 233, loop rollers 234, and registration rollers 235 are sequentially arranged from the upstream side to the downstream side. An S-shaped bending path 236 shown in FIG. 1 is also formed between the transport roller 231 and the transport roller 232. The bent path 236 describes a downward convex curve 237, and an upper guide plate 238 is provided on the upper side of the downward convex curve 237. The upper guide plate 238 serves to guide the sheet to the nip position of the conveying roller 232 so that the sheet does not turn up when the leading edge of the sheet passes the downward convex curve 237.

  A conveyance path (not shown) for conveying the sheet fed from the sheet storage unit 20 shown in FIG. 1 by the sheet feeding unit 21 joins the bending path 236.

  The transport rollers 231 to 233 and the loop roller 234 are configured to be movable by a known drive mechanism such as a solenoid and can be separated from the paper. A front end detection sensor 239 that is an optical sensor for detecting the front end of the sheet is provided at a position immediately before the registration roller 235. Further, the transport unit 23 is provided with a swing mechanism (not shown) that swings the registration roller 235 in the width direction of the paper (direction perpendicular to the drawing of FIG. 2).

  FIG. 3 shows the configuration of the control system of the image forming apparatus 1. The image forming apparatus 1 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs executed by the CPU 101, and a RAM (Random Access Memory) used as a work area of the CPU 101. 103. Furthermore, it has a hard disk drive (HDD) 104 as a mass storage device, an operation display unit 105, and a determination unit 106 for determining the paper type. As the ROM 102, an electrically erasable programmable ROM is usually used.

  The CPU 101 is an example of a control unit, and is connected to a ROM 102, a RAM 103, an HDD 104, an operation display unit 105, and a determination unit 106 via a system bus 107, and controls the entire apparatus. The CPU 101 is connected to the image reading unit 30, the image processing unit 110, the image forming unit 40, the paper feeding unit 21, and the transport unit 23 via the system bus 107.

  The HDD 104 stores image data of an original image obtained by reading by the image reading unit 30, or stores output image data and the like. The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 105 includes a plurality of keys, and receives input of various instructions, data such as characters and numbers by a user's key operation, and outputs an input signal. The data that can be input on the operation display unit 105 includes paper types of paper fed from the paper feeding unit 2 shown in FIG. 1 (thick paper, high stiffness paper, high friction resistance paper, or Data on whether paper other than thick paper, paper with low stiffness, or paper with low frictional resistance is also included.

  The image reading unit 30 optically reads a document image and converts it into an electrical signal. For example, when reading a color original, image data having luminance information of 10 bits for each of RGB per pixel is generated. Image data generated by the image reading unit 30 and image data transmitted from a PC (personal computer) 120 showing an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 110 for image processing. Is done. The image processing unit 110 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  In this example, a personal computer is used as an external device. However, the present invention is not limited to this, and various other devices such as a facsimile device can be used as the external device.

  For example, when a color image is formed by the image forming apparatus 1, R, G, B image data generated by the image reading unit 30 or the like is input to a color conversion LUT (look up table) in the image processing unit 110. Then, the image processing unit 110 performs color conversion on the R, G, and B data to Y, M, C, and Bk image data. Then, correction of gradation reproduction characteristics, screen processing such as halftone dots with reference to the density correction LUT, or edge processing for emphasizing thin lines is performed on the color-converted image data.

  The image forming unit 40 receives the image data processed by the image processing unit 110 and forms an image on the paper S.

  A signal indicating the detection result of the leading edge of the sheet by the leading edge detection sensor 239 illustrated in FIG. 2 is transmitted from the transport unit 23 to the CPU 101.

  When the CPU 101 transports the paper fed from the paper feeding unit 2 by the transport unit 23 to form an image, the CPU 101 determines the paper based on the user input result on the operation display unit 105 or the determination result of the determination unit 106. Paper type (thick paper, paper with high rigidity, or paper with high frictional resistance, or paper other than thick paper, paper with low rigidity, or paper with low frictional resistance).

  FIG. 4 shows the timing at which the CPU 101 separates the transport rollers 231-233 from the sheet when the determination result is a thick sheet, a sheet with high rigidity, or a sheet with a high frictional resistance value. FIG. 4 shows a state immediately after the leading edge of the sheet S being conveyed is nipped by the registration rollers 235 and the sheet S is nipped by all of the conveying rollers 231-233 and the loop roller 234. Based on the detection result of the leading edge of the sheet by the leading edge detection sensor 239 (not shown in FIG. 4) shown in FIG. 2, the CPU 101 conveys rollers 231-233 upstream of the loop roller 234 at this timing. Is moved away from the paper S by moving it in the direction of the arrow in the figure.

  On the other hand, if the determination result is a sheet other than thick paper, a sheet having low rigidity, or a sheet having a low frictional resistance value, the CPU 101 conveys upstream of the loop roller 234 immediately before the sheet enters the registration roller 235. All the rollers 231-233 are separated from the paper S. The separation timing of the transport rollers 231 to 233 is the same as the conventional timing shown in FIG.

  According to the image forming apparatus according to the first embodiment, when a stiff sheet such as a thick sheet, a sheet having high rigidity, or a sheet having a high frictional resistance is transported, the sheet is transported by the transport rollers 231-233. And it is conveyed to the registration roller 235 by the loop roller 234. Then, at the timing when the sheet is nipped by the registration rollers 235, the conveying rollers 231 to 233 are separated from the sheet. As a result, a stiff sheet comes into contact with the upper guide plate 238 of the S-shaped bending path 236 and the resistance of the sheet increases, so that even if a sudden load fluctuation or insufficient conveyance force occurs, the sheet is reliably conveyed. can do.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Note that in the second embodiment, redundant description of the same components as those in the first embodiment will be omitted. In the second embodiment, when the sheet fed from the sheet feeding unit 2 is transported by the transport unit 23 to form an image, processing executed by the CPU 101 to separate the transport rollers 231 to 233 from the sheet. However, this is different from the first embodiment. Other configurations are the same as those of the first embodiment.

  FIG. 5 shows a process in which the CPU 101 controls the conveyance unit 23 when the sheet fed from the sheet feeding unit 2 is conveyed by the conveyance unit 23 to form an image. In this process, the CPU 101 first determines that the paper type of the paper fed from the paper feeding unit 2 is thick paper based on the user input result on the operation display unit 105 or the discrimination result of the discrimination unit 106 shown in FIG. , It is determined whether the sheet is a sheet having a high rigidity or a sheet having a high frictional resistance value (abbreviated as a thick sheet in the figure) (step S1).

  If the determination result is a thick paper, a paper with high rigidity, or a paper with a high frictional resistance value, the CPU 101 starts transporting the paper by the transport rollers 231-233 and the loop roller 234 shown in FIG. 2 (step S 2).

  The CPU 101 confirms that the paper has arrived at the registration roller 235 based on the detection result of the front edge of the paper by the front edge detection sensor 239 shown in FIG. 2 (step S3). The conveyance by the roller 234 is continued, and a registration loop is formed on the sheet (step S4).

  Thereafter, the CPU 101 starts the rotation of the registration roller 235 (step S5), and separates the conveying rollers 231 to 233 and the loop roller 234 from the sheet (step S6). Subsequently, the CPU 101 corrects the position in the width direction of the sheet by swinging the registration roller 235 in the width direction of the sheet (step S7), and ends the process.

  If the determination result in step S1 is a sheet other than thick paper, that is, a sheet having low rigidity or a sheet having a low frictional resistance value, the CPU 101 starts conveyance of the sheet by the conveyance rollers 231 to 233 and the loop roller 234. (Step S8) After that, based on the detection result of the leading edge of the sheet by the leading edge detection sensor 239, all the conveying rollers 231 to 233 upstream from the loop roller 234 are all removed from the sheet S immediately before the sheet enters the registration roller 305. Separate (step S9). The separation timing of the transport rollers 231 to 233 is the same as the conventional timing shown in FIG.

  The CPU 101 confirms that the paper has arrived at the registration roller 235 based on the detection result of the front edge of the paper by the front edge detection sensor 239 (step S10). A loop is formed (step S11).

  Thereafter, the CPU 101 starts the rotation of the registration roller 235 (step S12) and moves the loop roller 234 away from the sheet (step S13). Subsequently, the CPU 101 corrects the position in the width direction of the sheet by swinging the registration roller 235 in the width direction of the sheet (step S14), and ends the process.

  FIG. 6 illustrates the timing at which the CPU 101 separates the transport rollers 231 to 233 from the sheet when the determination result in step S1 of FIG. 5 is a thick sheet, a sheet with high rigidity, or a sheet with a high frictional resistance value (FIG. 5). Step S6). In FIG. 6, the sheet S being conveyed is nipped by the registration rollers 235 and a registration loop is formed on the sheet S, and then the rotation of the registration rollers 235 is started, and the sheet S is conveyed by the conveyance rollers 231-233 and the loop rollers. 234 shows a state where all of 234 are nipped. At this timing, the CPU 101 separates the loop roller 234 from the paper S, and simultaneously moves the transport rollers 231-233 upstream from the loop roller 234 in the direction of the arrow to separate the paper from the paper S.

  According to the image forming apparatus according to the second embodiment, the transport rollers 231 to 233 and the loop roller are used when transporting stiff sheets such as thick paper, high rigidity paper, and high friction resistance paper. The sheet is conveyed to the registration roller 235 by the roller 234, the sheet is nipped by the registration roller 235, a registration loop is formed on the sheet by the loop roller 234, and then the rotation of the registration roller 235 is started. 233 is separated from the sheet simultaneously with the loop roller 234. As a result, when a stiff sheet is transported, the stiff sheet comes into contact with the upper guide plate 238 of the S-shaped bending path 236 and the resistance of the sheet increases, resulting in sudden load fluctuations and insufficient transport force. Even if it occurs, the sheet can be reliably conveyed.

[Modification]
The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention described in the claims.

  For example, in the above-described embodiment, the example in which the image forming unit 40 is provided with the four image forming units 40Y, 40M, 40C, and 40K to form a color image has been described. However, a single color in which only one image forming unit is provided. You may apply to the image forming apparatus which forms an image.

  Further, the example in which the intermediate transfer belt 50 is provided as a transfer material for transferring the toner image formed on the photoconductor 41 and the image is secondarily transferred from the intermediate transfer belt 50 to the paper S has been described. The present invention may be applied to an image forming apparatus that directly transfers a toner image.

  In the above-described embodiment, the CPU 101 determines the paper type (thick paper, high-stiffness paper, or frictional resistance value) of paper fed from the paper feed unit 2 based on the user input result on the operation display unit 105. Whether the paper is high, or is paper other than thick paper, paper with low rigidity, or paper with low frictional resistance). However, the present invention is not limited to this, and a detection unit that automatically detects the paper type of the paper fed from the paper feed unit 2 may be provided, and the paper type may be determined based on the detection result.

  In the first embodiment, the conveyance rollers 231 to 233 are separated from the paper at the timing when the paper is nipped by the registration rollers 235. In the second embodiment, the rotation of the registration roller 235 is performed. The conveyance rollers 231 to 233 are separated from the sheet at the start timing, but the intermediate timing between the first embodiment and the second embodiment (after the sheet is nipped by the registration roller 235, the registration roller The conveyance rollers 231 to 233 may be separated from the sheet until the rotation of the 235 starts.

  In the above-described embodiment, the present invention is applied to the image forming apparatus 1 having the S-shaped bent path 236 in the conveyance path of the sheet fed from the sheet feeding unit 2 that is mounted as an option. However, the present invention is not limited to this, and the present invention is applied to such an image forming apparatus when there is an image forming apparatus having an S-shaped bending path in the conveyance path of the sheet from the sheet storage unit in the image forming apparatus. Also good.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Document conveyance part, 20 ... Paper storage part, 21 ... Paper feed part, 22 ... Manual feed part, 23 ... Conveyance part, 30 ... Image reading part, 40 ... Image formation part, 40Y, 40M , 40C, 40K ... Image forming unit, 41 ... Photoconductor, 50 ... Intermediate transfer belt, 70 ... Secondary transfer unit, 80 ... Fixing unit, 101 ... CPU, 105 ... Operation display unit, 106 ... Discrimination unit, 231-233 ... Conveying roller, 234 ... Loop roller, 235 ... Registration roller, 236 ... S-shaped bending path, 237 ... Low convex curve, 238 ... Upper guide plate, 239 ... Tip detection sensor

Claims (4)

An image forming unit for forming a toner image on the image carrier;
A transfer portion for transferring the toner image onto a sheet;
A transport unit having a transport path bent in an S-shape for transporting paper toward the transfer unit;
A conveying roller, a loop roller, a registration roller, which are arranged in order from the upstream side along the conveying path;
A discriminating unit for discriminating whether the paper conveyed by the conveying unit is a predetermined first paper type or a predetermined second paper type;
If the determination unit determines that the sheet is the first sheet type, the conveyance roller is separated from the sheet before the sheet enters the registration roller, and the determination unit sets the sheet to the second sheet. A control unit that controls the conveying roller to be separated from the paper after the paper is nipped by the registration roller,
An image forming apparatus. When the determination unit determines that the sheet is the second sheet type, the control unit forms a registration loop on the sheet by the loop roller after the sheet is nipped by the registration roller, The image forming apparatus according to claim 1, wherein after the rotation of the registration roller is started, the loop roller and the conveyance roller are controlled to be separated from the sheet. The control unit controls to swing the registration roller after separating the loop roller and the conveyance roller from the sheet when the determination unit determines that the sheet is the second sheet type. The image forming apparatus according to claim 2. The image forming apparatus according to claim 1, wherein the second paper type is a paper thicker than the first paper type, a paper having a high rigidity, or a paper having a high frictional resistance value.