Transcription device, image forming apparatus

Abstract

To prevent transfer failure due to branching of transfer current during transfer of an image to a medium.SOLUTION: A transfer device comprises: a transfer barrel that is formed in its outer peripheral part with a groove-like recess extending in an axial direction and rotates around an axis, wherein a portion on the upstream side of the recess in the rotation direction is in contact with a medium to be conveyed; a sandwiching member that sandwiches the medium with the transfer barrel; application means that applies voltage to a nip part of the transfer barrel and the sandwiching member that sandwich the medium to transfer an image to the medium; and contact means that, at a transfer start time to start the transfer of the image to the medium, brings the sandwiching member into contact with only the portion of the transfer barrel on the upstream side of the recess in the rotation direction.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a transfer device and an image forming apparatus.

Background Art

[0002] Patent Document 1 describes a transfer device that transfers an image on an image carrier, and includes a transfer material conveying means that endlessly moves a transfer material along a circulating movement path, and a gripper piece that is attached to the conveying means, pivotally supported by a rotating shaft, rotates with respect to a base member, and grips the leading edge side of the transfer material, and a switch member attached to the base member. A transfer device is described in which the presence of the transfer material in the gripper is detected by partially cutting out the position of the switch member of the gripper piece.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to prevent transfer failure due to branching of the transfer current during image transfer to a medium.

Means for Solving the Problems

[0005] A transfer device according to a first aspect includes a transfer cylinder that rotates around the axis and has a groove-shaped recess extending in the axial direction on the outer peripheral portion, the transfer cylinder being in contact with a medium to be conveyed at a portion upstream in the rotation direction with respect to the recess, a sandwiching member that sandwiches the medium with the transfer cylinder, an applying means that applies a voltage to a nip portion between the transfer cylinder and the sandwiching member that sandwich the medium to transfer an image to the medium, and a contact means that brings the sandwiching member into contact only with the portion upstream in the rotation direction of the transfer cylinder with respect to the recess at the start of transfer when starting the transfer of the image to the medium.

[0006] The transfer device according to the second aspect is the transfer device described in the first aspect, wherein the contact means is configured by a member having a shape such that, at the start of transfer, the clamping member is non-contact with a portion on the downstream side in the rotational direction with respect to the concave portion on the transfer cylinder.

[0007] The transfer device according to the third aspect is the transfer device described in the second aspect, wherein the clamping member is columnar or cylindrical extending in the axial direction, and the contact means is configured such that an outer diameter of the clamping member is smaller than an opening width in the circumferential direction of the concave portion.

[0008] The transfer device according to the fourth aspect is the transfer device described in the first aspect, wherein the clamping member has a dimensional shape straddling the concave portion in the circumferential direction, and the contact means is configured such that image transfer to the medium is started after the state where the clamping member straddles the concave portion is eliminated.

[0009] The image forming apparatus according to the fifth aspect includes the transfer device according to any one of the first aspect to the fourth aspect, an image forming unit that forms an image to be transferred to the medium on the transfer device, and a conveyance unit that conveys the medium while gripping the medium with a gripping member that can be accommodated inside the concave portion to the nip portion.

Advantages of the Invention

[0010] The transfer device according to the first aspect prevents transfer failure due to branching of the transfer current during image transfer to the medium.

[0011] Compared with a configuration in which the contact means is a mechanism that moves the clamping member so as to be non-contact with a portion on the downstream side in the rotational direction with respect to the concave portion on the transfer cylinder at the start of transfer, the transfer device according to the second aspect suppresses transfer failure with a simple configuration.

[0012] Compared with a configuration in which the outer diameter of the clamping member is larger than the opening width in the circumferential direction of the concave portion of the transfer cylinder, the transfer device according to the third aspect suppresses transfer failure with a simple configuration.

[0013] The transfer device according to the fourth aspect prevents transfer failure due to the branching of the transfer current during image transfer to the medium in a configuration where the sandwiching member has a dimensional shape that straddles the concave portion in the circumferential direction.

[0014] The image forming apparatus according to the fifth aspect prevents image formation failure due to transfer failure during image transfer to the medium.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0016] An example of a transfer device and an image forming apparatus according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 11. In the figures, the arrow H indicates the vertical direction (up and down direction) of the apparatus, the arrow W indicates the width direction (horizontal direction) of the apparatus, and the arrow D indicates the depth direction (horizontal direction) of the apparatus.

[0017] (Image forming apparatus 10) The image forming apparatus 10 according to the present embodiment is an electrophotographic image forming apparatus that forms a toner image on a sheet member P as an example of a medium. As shown in FIG. 10, the image forming apparatus 10 includes a housing portion 50, a paper feeding mechanism 48, a chain gripper 66, a transfer device 30, an image forming portion 12, a fixing device 100, a cooling portion 90, a paper discharging mechanism 56, and a discharging portion 52.

[0018] 〔Housing portion 50〕 The housing portion 50 has a function of housing the sheet member P.

[0019] 〔Paper feeding mechanism 48〕 The paper feeding mechanism 48 has a function of conveying the sheet member P housed in the housing portion 50 to a chain gripper 66 described later.

[0020] Specifically, as shown in FIG. 10, the paper feeding mechanism 48 includes a delivery roll 62 and a plurality of conveying rolls 64 that convey the sheet member P along a paper feeding path 40 through which the sheet member P is conveyed.

[0021] The delivery roll 62 is a roll that sends out the sheet member P housed in the housing portion 50 to the paper feeding path 40. The plurality of conveying rolls 64 are rolls that convey the sheet member P sent out to the paper feeding path 40 by the delivery roll 62 to a chain gripper 66 described later.

[0022] [Chain gripper 66] The chain gripper 66 has a function of conveying the sheet member P conveyed from the paper feeding mechanism 48 to the paper discharge path 42 via a transfer device 30 and a fixing device 100 described later. The chain gripper 66 is an example of a conveying unit. As shown in FIG. 1, the chain gripper 66 includes a pair of chains 72, sprockets 71, 73, 92, 94, 96, and a gripping unit 68 (see FIG. 2) having a gripping member 76 for gripping the leading end of the sheet member P.

[0023] As shown in FIG. 2, the pair of chains 72 are arranged at intervals in the depth direction of the apparatus, and the chains 72 are formed in an endless shape (see FIG. 1). Then, as shown in FIG. 3, the pair of chains 72 are arranged on one axial end side and the other axial end side of an opposing roll 36 described later, and are wound around a pair of sprockets 73 having the axial direction as the depth direction of the apparatus. Further, as shown in FIG. 1, the pair of chains 72 are arranged on one axial end side and the other axial end side of a pressure roll 140 described later, and are wound around a pair of sprockets 71 having the axial direction as the depth direction of the apparatus. Furthermore, the pair of chains 72 are wound around a pair of sprockets 92, a pair of sprockets 94, and a pair of sprockets 96 arranged at intervals in the depth direction of the apparatus.

[0024] In this configuration, when a rotational force is transmitted to any one of the plurality of sprockets 71, 73, 92, 94, 96, the pair of chains 72 circulate in the direction of arrow C in the figure so as to move from the sprocket 73 side to the sprocket 71 side. In the present embodiment, the rotational force is transmitted to the sprocket 71. And in this configuration, the chain gripper 66 conveys the sheet member P gripped by the gripping unit 68 along the circulating direction of the pair of chains 72.

[0025] A plurality of gripping units 68 are provided and arranged at predetermined intervals along the circumferential direction (circular direction) of the chain 72. Further, as shown in FIG. 2, the gripping unit 68 extends in the depth direction of the apparatus, and both portions on both sides of the gripping unit 68 in the depth direction of the apparatus are respectively attached to a pair of chains 72. The gripping unit 68 moves along the circumferential direction of the chain 72 as the chain 72 rotates.

[0026] The gripping unit 68 includes a plate portion 80 extending in the depth direction of the apparatus as shown in FIG. 2, a pair of support plates 82 supporting the plate portion 80, and shaft members 84 extending in the depth direction of the apparatus and having ends respectively attached to the chain 72. Further, the gripping unit 68 includes a gripping member 76 that grips the tip of the sheet member P between the plate portion 80.

[0027] The plate portion 80 is made of stainless steel and is disposed between the pair of chains 72. Further, when viewed from the depth direction of the apparatus, the upstream portion in the sheet conveyance direction of the plate portion 80 is inclined with respect to the sheet conveyance direction so as to approach the sheet member P relative to the downstream portion.

[0028] The support plates 82 are made of stainless steel and are respectively disposed at both ends of the plate portion 80 with the plate thickness direction as the depth direction of the apparatus. Both ends of the plate portion 80 are respectively attached to the pair of support plates 82, and the pair of support plates 82 support the plate portion 80. Further, circular through-holes 82a are formed in the support plates 82.

[0029] The shaft members 84 are made of stainless steel, extend in the depth direction of the apparatus, and are disposed on the downstream side in the sheet conveyance direction with respect to the plate portion 80. Further, the shaft members 84 respectively pass through the through-holes 82a formed in the support plates 82. Both ends of the shaft members 84 are respectively attached to the pair of chains 72.

[0030] A plurality of gripping members 76 are provided and attached to the shaft member 84 at predetermined intervals along the depth direction of the apparatus. The gripping member 76 includes a main body portion 86 in which a through hole 86a through which the shaft member 84 passes is formed, and a contact portion 88 that contacts the sheet member P.

[0031] The main body portion 86 is made of aluminum. When viewed from the depth direction of the apparatus, the downstream portion of the main body portion 86 in the sheet conveyance direction is formed in an arc shape. Further, on the upstream side of the main body portion 86 in the sheet conveyance direction and on the outer side of the endless chain 72 (the side opposite to the side surrounded by the endless chain 72 when viewed from the depth direction of the apparatus), a protruding portion 86b that protrudes toward the plate portion 80 is formed. The protruding portion 86b is formed in a rectangular shape when viewed from the protruding direction.

[0032] The contact portion 88 is a plate member made of stainless steel and is attached to the surface of the protruding portion 86b facing the outer side of the endless chain 72. The contact portion 88 extends from the protruding portion 86b toward the plate portion 80 and comes into contact with the plate portion 80 from the outer side of the endless chain 72.

[0033] In this configuration, the shaft member 84 is rotated by a cam mechanism (not shown), and the contact portion 88 is pressed from the outer side of the endless chain 72 toward the plate portion 80 to contact the plate portion 80, and the contact portion 88 is separated from the plate portion 80. In this way, the leading end of the sheet member P is gripped and the gripping is released by the gripping member 76.

[0034] 〔Transfer device 30〕 The transfer device 30 has a function of superimposing and primarily transferring the toner images of the photosensitive drums 21 of each color described later onto the intermediate transfer member, and secondarily transferring the superimposed toner images onto the sheet member P. As shown in FIG. 1, the transfer device 30 includes a transfer belt 31 as an intermediate transfer member, a plurality of rolls 32, a primary transfer roll 33, a secondary transfer roll 34, and an opposing roll 36. Further, the transfer device 30 includes an application roll 44 that applies a voltage to the secondary transfer roll 34.

[0035] As shown in Fig. 1, the transfer belt 31 is endless and is wound around a plurality of rolls 32 and a secondary transfer roll 34 so as to have an inverted triangular shape when viewed from the front. The transfer belt 31 circulates in the direction of arrow B when at least one of the plurality of rolls 32 is rotationally driven. The photosensitive drums 21 of each color are arranged on the outer peripheral portion of the transfer belt 31.

[0036] The primary transfer roll 33 is arranged on the opposite side of the photosensitive drums 21 of each color with the transfer belt 31 interposed therebetween. The primary transfer roll 33 has a function of transferring the toner image formed on the photosensitive drum 21 to the transfer belt 31 at the primary transfer position T between the photosensitive drum 21 and the primary transfer roll 33.

[0037] The secondary transfer roll 34 is arranged so as to push out the inclined portion on one side (left side in the figure) in the device width direction of the transfer belt 31.

[0038] The secondary transfer roll 34 around which the transfer belt 31 is wound forms a nip portion NT between the secondary transfer roll 34 and an opposing roll 36 (details will be described later) arranged on the opposite side of the secondary transfer roll 34 with the transfer belt 31 interposed therebetween. In other words, the nip portion NT is formed between the opposing roll 36 and the secondary transfer roll 34. The secondary transfer roll 34 around which the transfer belt 31 is wound sandwiches the sheet member P conveyed by the chain gripper 66 with the opposing roll 36. The secondary transfer roll 34 is an example of a sandwiching member. The opposing roll 36 is an example of a transfer cylinder.

[0039] The application roll 44 has a smaller diameter than the secondary transfer roll 34 and is arranged on the opposite side of the transfer belt 31 with the secondary transfer roll 34 interposed therebetween as shown in Fig. 2. The application roll 44 extends in the depth direction of the device and is in contact with the secondary transfer roll 34.

[0040] In this configuration, the application roll 44 rotates following the rotation of the rotating secondary transfer roll 34. Further, the application roll 44 applies a voltage to the secondary transfer roll 34 by being supplied with power from a power source (not shown) to the shaft portion of the application roll 44. By applying a voltage to the secondary transfer roll 34, the application roll 44 forms a transfer electric field for transferring the toner image on the transfer belt 31 to the sheet member P in the nip portion NT between the secondary transfer roll 34 and the opposing roll 36. That is, the application roll 44 causes the toner image on the transfer belt 31 to be transferred to the sheet member P. The application roll 44 is an example of an application means.

[0041] 〔Image forming unit 12〕 The image forming unit 12 has a function of forming an image to be transferred to the sheet member P by an electrophotographic method. As shown in FIG. 10, the image forming unit 12 is arranged on the other side (the right side in the figure) in the apparatus width direction with respect to the paper feeding mechanism 48. The image forming unit 12 includes a plurality of toner image forming units 20 for forming a toner image.

[0042] A plurality of toner image forming units 20 are provided so as to form toner images for each color. In the present embodiment, a total of four toner image forming units 20 for yellow (Y), magenta (M), cyan (C), and black (K) are provided. (Y), (M), (C), and (K) shown in FIGS. 1 and 10 indicate the constituent parts corresponding to the respective colors.

[0043] -Toner image forming unit 20- The toner image forming units 20Y, 20M, 20C, and 20K are basically the same in configuration except for the toner used. The toner image forming units 20Y, 20M, 20C, and 20K each include a photosensitive drum 21 corresponding to each color.

[0044] As shown in FIGS. 1 and 10, the toner image forming units 20Y and 20M are arranged side by side along the horizontal portion of the transfer belt 31 in an inverted triangular posture. The toner image forming units 20C and 20K are arranged side by side along the inclined portion on the other side (the right side in the figure) in the apparatus width direction of the transfer belt 31.

[0045] The toner image forming units 20Y, 20M, 20C, and 20K form toner images by attaching toners of respective colors Y, M, C, and K to the outer peripheral surfaces of the respective photoreceptor drums 21. The toner images formed on the respective photoreceptor drums 21 are transferred to the transfer belt 31 at the primary transfer position T between the respective photoreceptor drums 21 and the primary transfer roll 33. That is, the image forming unit 12 including the toner image forming unit 20 forms a toner image on the transfer belt 31.

[0046] 〔Fixing device 100〕 The fixing device 100 has a function of fixing the toner image transferred to the sheet member P by the transfer device 30 to the sheet member P.

[0047] As shown in FIG. 1, the fixing device 100 includes a preheating unit 102 that preheats the sheet member P conveyed by the chain gripper 66, a main heating unit 120 that heats the sheet member P, and a blowing unit 170 that blows air onto the sheet member P.

[0048] -Preheating unit 102- As shown in FIG. 1, the preheating unit 102 is disposed on the downstream side of the nip portion NT in the conveyance direction of the sheet member P (hereinafter referred to as "sheet conveyance direction") so as to face the upper surface side of the conveyed sheet member P. The preheating unit 102 includes a reflecting member 104, a plurality of infrared heaters 106 (hereinafter referred to as "heaters 106"), and a wire mesh 112.

[0049] In this configuration, the preheating unit 102 non - contact heats the sheet member P conveyed by the circulating chain 72 from the thickness direction of the sheet member P.

[0050] -Blowing unit 170- As shown in FIG. 1, the spraying unit 170 is arranged to face the preheating unit 102 in the thickness direction of the conveyed sheet member P, and the conveyed sheet member P passes between the spraying unit 170 and the preheating unit 102. Further, the spraying unit 170 includes a plurality of fans 172 arranged in the width direction of the conveyed sheet member P and in the sheet conveying direction.

[0051] In this configuration, the plurality of fans 172 spray air toward the conveyed sheet member P, thereby stabilizing the conveying posture of the conveyed sheet member P.

[0052] -Main heating unit 120- As shown in FIG. 1, the main heating unit 120 is arranged on the downstream side of the preheating unit 102 in the sheet conveying direction. The main heating unit 120 includes a heating roll 130 that contacts the conveyed sheet member P and heats the sheet member P, and a pressure roll 140 that presses the sheet member P toward the heating roll 130. Further, the main heating unit 120 further includes a driven roll 150 that rotates following the heating roll 130 and heats the heating roll 130.

[0053] In this configuration, the heating roll 130 and the pressure roll 140 sandwich and convey the sheet member P onto which the toner image has been transferred, so that the toner image is heated and fixed to the sheet member P.

[0054] 〔Cooling unit 90〕 The cooling unit 90 has a function of cooling the sheet member P heated by the fixing device 100. As shown in FIG. 10, a paper discharge path 42 is formed through which the sheet member P on which the toner image is fixed by the fixing device 100 and discharged to the outside of the apparatus main body 10a is conveyed, and the cooling unit 90 is arranged along this paper discharge path 42.

[0055] As shown in FIG. 11, the cooling unit 90 includes two rolls 90a arranged in the apparatus width direction, and an endless belt 90b wound around the two rolls 90a and having an upper surface along the paper discharge path 42. Further, the cooling unit 90 includes a cooling fan 90c that blows air against the lower surface of the belt 90b to cool the belt 90b, and rolls 90d respectively arranged on the opposite sides of the two rolls 90a with the paper discharge path 42 and the belt 90b interposed therebetween.

[0056] In this configuration, one of the two rolls 90a is rotationally driven. As a result, the belt 90b cooled by the cooling fan 90c circulates in the direction of the arrow in the figure, so that the roll 90d rotates following the circulating belt 90b. Further, the circulating belt 90b and the roll 90d that rotates following it sandwich and convey the sheet member P. Thereby, the sheet member P is cooled.

[0057] 〔Paper discharge mechanism 56〕 The paper discharge mechanism 56 has a function of discharging the sheet member P cooled by the cooling unit 90 to the discharge unit 52 outside the apparatus main body 10a. As shown in FIG. 10, the paper discharge mechanism 56 is arranged on one side (the left side in the figure) in the apparatus width direction with respect to the image forming unit 12. Further, the paper discharge mechanism 56 includes a plurality of conveying rolls 54 that convey the sheet member P along the paper discharge path 42.

[0058] (Main part configuration) Next, the opposing roll 36, the secondary transfer roll 34, and the contact means 190 that constitute the transfer device 30 will be described. The contact means 190 has a configuration in which, at the start of transfer (details will be described later), the secondary transfer roll 34 is brought into contact only with a portion on the upstream side in the rotation direction of the opposing roll 36 with respect to a recess 178 described later.

[0059] 〔Opposing roll 36〕 As described above, the opposing roll 36 is arranged on the opposite side of the secondary transfer roll 34 with the transfer belt 31 interposed therebetween (see FIG. 1). And as shown in FIG. 3, the opposing roll 36 extends in the apparatus depth direction.

[0060] The opposing roll 36 is made of aluminum and has a cylindrical roll portion 174 and a pair of shaft portions 176 that respectively project in the depth direction of the apparatus from both end portions of the roll portion 174. The roll portion 174 is an example of an outer peripheral portion. The sprocket 73 described above is respectively attached to the pair of shaft portions 176.

[0061] The opposing roll 36 is driven following the circulation of the chain 72 of the chain gripper 66 and rotates along the circulation direction C of the chain 72 (in the direction of arrow R shown in FIG. 6).

[0062] As shown in FIG. 4, a recess 178 capable of accommodating the gripping member 76 inside is formed in the roll portion 174 of the opposing roll 36. This recess 178 has a groove-like shape extending in the depth direction of the apparatus from one end to the other end of the roll portion 174. In the recess 178, the opening edge on the upstream side in the rotation direction of the opposing roll 36 is the opening edge 178A, and the opening edge on the downstream side in the rotation direction of the opposing roll 36 is the opening edge 178B. The distance in the rotation direction (circumferential direction) of the opposing roll 36 between the opening edges 178A and 178B is defined as the opening width L.

[0063] 〔Secondary transfer roll 34〕 As described above, the secondary transfer roll 34 is disposed on the opposite side of the opposing roll 36 with the transfer belt 31 interposed therebetween (see FIG. 1). As shown in FIG. 3, the secondary transfer roll 34 includes a shaft member 34a extending in the depth direction of the apparatus and a cylindrical roll portion 34b extending in the depth direction of the apparatus and through which the shaft member 34a passes. Note that the roll portion 34b may be cylindrical.

[0064] The shaft member 34a is a conductor shaft, and both end portions of the shaft member 34a are supported by a frame (not shown) via bearings. Note that the shaft member 34a may be a conductor, preferably a metal, and more preferably stainless steel.

[0065] The roll portion 34b is made of rubber and is attached to the shaft member 34a so as to rotate together with the shaft member 34a. The roll portion 34b is arranged so as to be accommodated inside the roll portion 174 of the opposing roll 36 in the depth direction of the apparatus.

[0066] In the present embodiment, as shown in FIG. 4, the outer diameter A of the roll portion 34b is smaller than the opening width L in the circumferential direction of the concave portion 178 of the opposing roll 36.

[0067] By setting the relationship between the outer diameter A of the roll portion 34b of the secondary transfer roll 34 described above and the opening width L of the concave portion 178 of the opposing roll 36, when the secondary transfer roll 34 is in contact with either one of the opening edges 178A and 178B of the concave portion 178, it is not in contact with the other. Specifically, as shown in FIG. 6, when the secondary transfer roll 34 is in contact with the portion on the downstream side in the rotation direction with respect to the concave portion 178 of the opposing roll 36, it is not in contact with the portion on the upstream side in the rotation direction with respect to the concave portion 178 of the opposing roll 36. Further, as shown in FIG. 7, when the secondary transfer roll 34 is in contact with the portion on the upstream side in the rotation direction with respect to the concave portion 178 of the opposing roll 36, it is not in contact with the portion on the downstream side in the rotation direction with respect to the concave portion 178 of the opposing roll 36. The setting that the outer diameter A of the roll portion 34b of the secondary transfer roll 34 in the present embodiment is smaller than the opening width L of the concave portion 178 of the opposing roll 36 constitutes the contact means 190 in the present embodiment.

[0068] (Transfer operation to the sheet member P) Next, the transfer operation of the toner image to the sheet member P in the image forming apparatus 10 and the transfer apparatus 30 of the present embodiment will be described.

[0069] First, the image forming unit 12 forms toner images of respective colors on the photosensitive drums 21 of the toner image forming units 20Y, 20M, 20C, and 20K, and superimposes the toner images of respective colors on the transfer belt 31 for primary transfer.

[0070] The sheet member P is sent out from the storage unit 50 by the feeding roll 62 into the paper feeding path 40, conveyed by the conveying roll 64, and delivered to the chain gripper 66. The sheet member P delivered to the chain gripper 66 is conveyed toward the nip portion NT between the secondary transfer roll 34 around which the transfer belt 31 is wound and the opposing roll 36. At this time, the gripping member 76 of the chain gripper 66 grips the leading end of the sheet member P (see Fig. 2).

[0071] As shown in Fig. 5, when the gripping member 76 that grips the sheet member P reaches the opposing roll 36, it is housed inside the recess 178 of the roll portion 174. The chain gripper 66 conveys the sheet member P toward the nip portion NT with the gripping member 76 housed inside the recess 178. The opposing roll 36 is driven by the rotation of the chain 72 of the chain gripper 66 and rotates with the gripping member 76 housed inside the recess 178. At this time, as shown in Figs. 6 and 7, the opposing roll 36 conveys the sheet member P gripped by the gripping member 76 to the nip portion NT while winding it around the rotating roll portion 174. Also, at this time, the secondary transfer roll 34 is in contact with the portion of the opposing roll 36 on the downstream side in the rotation direction with respect to the recess 178, sandwiching the transfer belt 31.

[0072] With the rotation of the opposing roll 36 from this state, the portion of the opposing roll 36 in contact with the secondary transfer roll 34 changes from the portion on the downstream side in the rotation direction with respect to the recess 178 to the portion on the upstream side in the rotation direction with respect to the recess 178, as shown in Figs. 6 and 7.

[0073] When the secondary transfer roll 34 around which the transfer belt 31 is wound contacts the opening edge 178A of the concave portion 178, the secondary transfer roll 34 is in a state of sandwiching the sheet member P gripped by the gripping member 76 with the opposing roll 36, as shown in FIG. 7. At this time, a voltage is applied to the nip portion NT between the secondary transfer roll 34 and the opposing roll 36 that sandwich the sheet member P by the application roll 44, and a transfer electric field is formed. By forming a transfer electric field in the nip portion NT, the transfer of the toner image on the transfer belt 31 wound around the secondary transfer roll 34 to the sheet member P is started. In this specification, the time when a transfer electric field is formed in the nip portion NT between the secondary transfer roll 34 and the opposing roll 36 that sandwich the sheet member P and the transfer of the toner image on the transfer belt 31 to the sheet member P is started is referred to as the start of transfer.

[0074] At the start of transfer, the secondary transfer roll 34 contacts only the portion of the opposing roll 36 on the upstream side in the rotation direction with respect to the concave portion 178 due to the shape of the secondary transfer roll 34 and the shape of the concave portion 178 described above.

[0075] After the start of transfer, the toner image on the transfer belt 31 is transferred to the sheet member P along with the circulation of the chain gripper 66, the circulation of the transfer belt 31, and the rotation of the opposing roll 36. The gripping member 76 accommodated inside the concave portion 178 of the opposing roll 36 is released from the concave portion 178 as the opposing roll 36 rotates, as shown in FIG. 8. The gripping member 76 released from the concave portion 178 moves along the circumferential direction (arrow C) of the chain 72 and conveys the sheet member P. When the conveyed sheet member P detaches from the nip portion NT, the transfer of the toner image to the sheet member P in the transfer device 30 is completed.

[0076] <Operation and Effect> Next, the operation and effect of this embodiment will be described. In this description, when describing a comparative form with respect to this embodiment, when using components and the like similar to those of the image forming apparatus 10 of this embodiment, the reference numerals and names of those components and the like will be used as they are for the description.

[0077] The transfer device 30 of the image forming apparatus 10 according to the present embodiment includes a contact means 190 that, at the start of transfer, brings the secondary transfer roll 34 into contact only with a portion of the opposing roll 36 on the upstream side in the rotational direction with respect to the recess 178. The image forming apparatus 10 according to the present embodiment is compared with an image forming apparatus 210 of a comparative form described below.

[0078] As shown in FIG. 9, the image forming apparatus 210 of the comparative form includes a transfer device 230 in which, at the start of transfer, the secondary transfer roll 234 comes into contact with portions on both sides of the opposing roll 36 with respect to the recess 178, instead of the transfer device 30 of the image forming apparatus 10. Specifically, the transfer device 230 of the comparative form includes a secondary transfer roll 234 in which the outer diameter of the roll portion 234b is larger than the opening width L of the recess 178, instead of the secondary transfer roll 34. That is, the transfer device 230 of the comparative form does not include the contact means 190. Except for the above points, the image forming apparatus 210 of the comparative form has the same configuration as the image forming apparatus 10 of the present embodiment.

[0079] At the start of transfer, in the transfer device 230 of the comparative form, the secondary transfer roll 234 is in contact with portions on both sides of the opposing roll 36 with respect to the recess 178. At this time, when a current flows through the secondary transfer roll 234 due to the application of the voltage of the application roll 44, the current branches at the start of transfer into a current flowing through the sheet member P and a current flowing through a portion of the opposing roll 36 on the downstream side in the rotational direction with respect to the recess 178. Therefore, in the transfer device 230 of the comparative form, the transfer electric field formed in the sheet member P at the start of transfer is smaller than the transfer electric field formed when all the current flowing from the application roll 44 flows through the sheet member P and to the opposing roll 36 with the sheet member P interposed therebetween. If the transfer electric field formed in the sheet member P is small, there is a risk of transfer failure of the toner image formed on the transfer belt 31 to the sheet member P. Further, there is a risk that image formation failure due to transfer failure may occur in the image forming apparatus 210 including the transfer device 230 of the comparative form during image transfer to the sheet member P.

[0080] On the other hand, the transfer device 30 of the present embodiment includes a contact means 190. Specifically, at the start of transfer, the secondary transfer roll 34 contacts only the upstream portion in the rotation direction of the opposing roll 36 with respect to the concave portion 178, and does not contact the downstream portion in the rotation direction with respect to the concave portion 178. As a result, all the current flowing from the application roll 44 to the secondary transfer roll 34 flows to the opposing roll 36 across the sheet member P at the start of transfer, and the transfer electric field formed in the sheet member P does not decrease. Therefore, by including the contact means 190, the transfer device 30 of the present embodiment prevents transfer failure due to the branching of the transfer current during image transfer to the sheet member P.

[0081] In addition, the image forming apparatus 10 including the transfer device 30 of the present embodiment prevents image formation failure due to transfer failure during image transfer to the sheet member P.

[0082] Further, the transfer device 30 of the present embodiment has a shape such that the secondary transfer roll 34 is non-contact with the downstream portion in the rotation direction with respect to the concave portion 178 in the opposing roll 36 at the start of transfer, thereby constituting the contact means 190. Therefore, compared with a configuration in which the contact means is a mechanism that moves the secondary transfer roll so as to be non-contact with the downstream portion in the rotation direction with respect to the concave portion in the opposing roll at the start of transfer, the transfer device 30 of the present embodiment suppresses transfer failure with a simple configuration.

[0083] Moreover, the transfer device 30 of the present embodiment constitutes the contact means 190 because the outer diameter A of the roll portion 34b is smaller than the opening width L in the circumferential direction of the concave portion 178 of the opposing roll 36. Therefore, compared with a configuration in which the outer diameter of the secondary transfer roll is larger than the opening width in the circumferential direction of the concave portion of the opposing roll, the transfer device 30 of the present embodiment suppresses transfer failure with a simple configuration.

[0084] <Second Embodiment> Next, an example of a transfer device and an image forming apparatus according to the second embodiment of the present invention will be described with reference to FIG. 12. Regarding the second embodiment, different parts from the first embodiment will be mainly described. Further, in the description of the second embodiment, when using the same components as those described in the image forming apparatus 10 of the first embodiment, the reference numerals and names of those components will be used as they are for the description.

[0085] (Image forming apparatus 310) The image forming apparatus 310 includes a transfer device 330 instead of the transfer device 30 in the image forming apparatus 10. As shown in FIG. 12, the transfer device 330 includes a secondary transfer roll 334 instead of the secondary transfer roll 34 in the transfer device 30. The secondary transfer roll 334 is an example of a sandwiching member. Further, the transfer device 330 further includes a switching unit 360 that switches ON / OFF of voltage application by the application roll 44 according to the state of the secondary transfer roll 334.

[0086] 〔Secondary transfer roll 334〕 The secondary transfer roll 334 includes a cylindrical roll portion 334b instead of the roll portion 34b in the secondary transfer roll 34. Note that the roll portion 334b may be cylindrical.

[0087] In the present embodiment, as shown in FIG. 12, the outer diameter A2 of the roll portion 334b is larger than the opening width L in the circumferential direction of the concave portion 178 of the opposing roll 36.

[0088] The secondary transfer roll 334 around which the transfer belt 31 is wound forms a contact portion NT2 between the secondary transfer roll 334 and the opposing roll 36 disposed on the opposite side of the secondary transfer roll 334 with the transfer belt 31 interposed therebetween. The contact width LN, which is the distance between both end portions of the contact portion NT2 in the circumferential direction of the opposing roll 36, is larger than the opening width L of the concave portion 178. That is, the secondary transfer roll 334 in the present embodiment has a dimensional shape that straddles the concave portion 178 in the circumferential direction.

[0089] 〔Switching unit 360〕 The switching unit 360 is configured to include detection means (not shown). The detection means (not shown) includes, for example, a paper sensor disposed between the paper feed path 40 and the opposing roll 36. The switching unit 360 is configured to turn off the application of voltage by the application roll 44 except when the toner image is transferred to the sheet member P. The switching unit 360 is configured to turn on the application of voltage by the application roll 44 after a predetermined time has elapsed since the paper sensor of the detection means detects the leading edge of the sheet member P. The predetermined time is the time required for the leading edge of the sheet member P to be conveyed to a position where it is sandwiched between the secondary transfer roll 334 that contacts only the upstream portion in the rotational direction with respect to the concave portion 178 of the opposing roll 36 and the opposing roll 36 from the detection position by the paper sensor. In other words, the switching unit 360 turns off the application of voltage by the application roll 44 when the secondary transfer roll 334 sandwiches the leading edge of the sheet member P with the opposing roll 36 and contacts both sides in the rotational direction with respect to the concave portion 178 of the opposing roll 36.

[0090] By turning on the application of voltage by the application roll 44 at the above timing, the switching unit 360 forms a transfer electric field in the contact portion NT2, and starts the transfer of the toner image on the transfer belt 31 wound around the secondary transfer roll 334 to the sheet member P. That is, in the present embodiment, the time when the switching unit 360 turns on the application of voltage by the application roll 44 is the start time of transfer. Also, by turning on the application of voltage by the application roll 44 at this timing, the secondary transfer roll 334 contacts only the upstream portion in the rotational direction with respect to the concave portion 178 of the opposing roll 36 at the start of transfer. The switching unit 360 of the present embodiment is an example of the contact means.

[0091] From the start of transfer until the sheet member P separates from the contact portion NT2, the switching unit 360 keeps the application of voltage by the application roll 44 on. When the sheet member P separates from the contact portion NT2, the switching unit 360 turns off the application of voltage by the application roll 44.

[0092] Except for the above points, the image forming apparatus 310 of the second embodiment has the same configuration as the image forming apparatus 10 of the first embodiment.

[0093] (Transfer operation to the sheet member P) Next, the transfer operation of the toner image to the sheet member P in the image forming apparatus 310 and the transfer apparatus 330 of the present embodiment will be described.

[0094] First, the image forming unit 12 forms toner images of respective colors on the photoreceptor drums 21 of the toner image forming units 20Y, 20M, 20C, and 20K, and superposes the toner images of respective colors on the transfer belt 31 for primary transfer.

[0095] The sheet member P is sent out from the storage unit 50 to the paper feed path 40 by the feed roll 62, conveyed by the conveyance roll 64, and delivered to the chain gripper 66. The sheet member P delivered to the chain gripper 66 is conveyed toward the contact portion NT2 between the secondary transfer roll 334 around which the transfer belt 31 is wound and the opposing roll 36. At this time, the gripping member 76 of the chain gripper 66 grips the leading end of the sheet member P (see FIG. 2).

[0096] When the gripping member 76 that grips the sheet member P reaches the opposing roll 36, it is accommodated inside the concave portion 178 of the roll portion 174. The chain gripper 66 conveys the sheet member P toward the contact portion NT2 in a state where the gripping member 76 is accommodated inside the concave portion 178. The opposing roll 36 is driven following the circulation of the chain 72 of the chain gripper 66 and rotates in a state where the gripping member 76 is accommodated inside the concave portion 178. At this time, the opposing roll 36 conveys the sheet member P gripped by the gripping member 76 to the contact portion NT2 while winding it around the rotating roll portion 174. Also, at this time, the secondary transfer roll 334 is in contact with a portion of the opposing roll 36 on the downstream side in the rotation direction with respect to the concave portion 178, with the transfer belt 31 interposed therebetween. At this time, the application of the voltage by the application roll 44 is turned off by the switching unit 360.

[0097] As the opposing roll 36 rotates from this state, the secondary transfer roll 336 transitions to a state where the portion in contact with the opposing roll 36 straddles the concave portion 178 in the circumferential direction, as shown in FIG. 12. At this time, the secondary transfer roll 334 sandwiches the sheet member P with the opposing roll 36 and is in a state of contacting the portions on both circumferential sides of the concave portion 178 in the opposing roll 36. Therefore, the application of voltage by the application roll 44 remains OFF by the switching unit 360.

[0098] After that, as the opposing roll 36 rotates, the secondary transfer roll 336 transitions to a state where it contacts only the portion on the upstream side in the rotation direction with respect to the concave portion 178 in the opposing roll 36 while still sandwiching the sheet member P with the opposing roll 36, as shown in FIG. 12. At this time, the application of voltage by the application roll 44 is switched ON by the switching unit 360, and the transfer of the toner image on the transfer belt 31 wound around the secondary transfer roll 334 to the sheet member P is started. That is, the switching unit 360 is configured such that the transfer of the toner image to the sheet member P is started after the state where the secondary transfer roll 334 straddles the concave portion 178 is eliminated.

[0099] Then, the gripping member 76 housed inside the concave portion 178 of the roll portion 174 is released from the concave portion 178 as the opposing roll 36 rotates, as shown in FIG. 8. The gripping member 76 released from the concave portion 178 moves along the circumferential direction (arrow C) of the chain 72 and conveys the sheet member P. The switching unit 360 keeps the application of voltage by the application roll 44 ON until the sheet member P gripped by the gripping member 76 separates from the contact portion NT2. After the sheet member P gripped by the gripping member 76 separates from the contact portion NT2, the switching unit 360 switches the application of voltage by the application roll 44 to OFF.

[0100] <Operation and Effect> Next, the operation and effect of this embodiment will be described.

[0101] The transfer device 330 of this embodiment includes a switching unit 360 configured such that after the state where the secondary transfer roll 334 straddles the concave portion 178 is eliminated, the transfer of the toner image to the sheet member P is started. As a result, all the current flowing from the application roll 44 to the secondary transfer roll 34 flows to the opposing roll 36 across the sheet member P at the start of the transfer. Therefore, by including the switching unit 360, the transfer device 30 of this embodiment prevents transfer defects due to the branching of the transfer current during the transfer of the image to the sheet member P.

[0102] Further, the image forming apparatus 310 including the transfer device 330 of this embodiment prevents image formation defects due to transfer defects during the transfer of the image to the sheet member P.

[0103] As described above, specific embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications, changes, and improvements are possible within the scope of the technical idea of the present invention.

[0104] For example, in the above embodiment, the sandwiching members are the columnar or cylindrical secondary transfer rolls 34 and 334. However, the sandwiching members in the present invention are not limited to columnar or cylindrical ones. The sandwiching members in the present invention may be, for example, a charger around which the transfer belt 31 is wound.

[0105] Also, in the above embodiment, the applying means is the applying roll 44 that applies a voltage to the secondary transfer rolls 34 and 334. However, the applying means in the present invention is not limited to the one that applies a voltage to the secondary transfer rolls 34 and 334. The applying means in the present invention may be, for example, a configuration that applies a voltage of the opposite polarity to the applying roll 44 to the opposing roll 36 instead of the applying roll 44.

[0106] Also, in a configuration where the secondary transfer roll has a dimensional shape that straddles the concave portion of the opposing roll in the circumferential direction, if the transfer to the sheet member is started after the state where the secondary transfer roll straddles the concave portion is eliminated, the contact means in this configuration is not limited to the switching portion 360 of the second embodiment. For example, a form in which a voltage is constantly applied to the secondary transfer roll by the application roll, and after the state where the secondary transfer roll straddles the concave portion is eliminated, the toner image on the transfer belt reaches the sheet member and the transfer of the toner image is started is also included in the technical idea of the present invention. In this form, after the state where the secondary transfer roll straddles the concave portion is eliminated, an image forming unit that forms a toner image on the transfer belt so that the toner image on the transfer belt reaches the sheet member and the transfer of the toner image is started serves as an example of the contact means.

Explanation of Signs

[0107] 10 Image forming apparatus 12 Image forming unit 30 Transfer apparatus 34 Secondary transfer roll (an example of a sandwiching member) 36 Opposing roll (an example of a transfer cylinder) 44 Application roll (an example of application means) 66 Chain gripper (an example of a conveyance unit) 174 Roll portion (an example of an outer peripheral portion) 178 Concave portion 190 Contact means 310 Image forming apparatus 330 Transfer apparatus 334 Secondary transfer roll (an example of a sandwiching member) 360 Switching portion (an example of contact means) A Outer diameter (a part of contact means) L Opening width (a part of contact means) NT Nip portion P Sheet member (an example of a medium)

Claims

1. A transfer cylinder having a groove-shaped recess extending in the axial direction on the outer peripheral portion, and rotating around the axis, wherein a portion on the upstream side in the rotation direction with respect to the recess contacts the medium to be conveyed; A sandwiching member that sandwiches the medium with the transfer cylinder; Applying means for applying a voltage to the nip portion between the transfer cylinder and the sandwiching member sandwiching the medium to transfer an image to the medium; Contacting means for contacting the sandwiching member only with a portion on the upstream side in the rotation direction with respect to the recess of the transfer cylinder at the start of transfer when starting the transfer of the image to the medium; comprising: The sandwiching member is columnar or cylindrical and extends in the axial direction, and an outer diameter of the sandwiching member is larger than an opening width in the circumferential direction of the recess, and has a dimensional shape straddling the recess in the circumferential direction; The contacting means is configured to apply a voltage to the nip portion between the transfer cylinder and the sandwiching member by the applying means after the state in which the sandwiching member straddles the recess is eliminated, so that the transfer of the image to the medium is started. A transfer device.

2. The transfer device according to claim 1; An image forming unit that forms an image to be transferred to the medium on the transfer device; A conveying unit that conveys the medium to the nip portion while gripping the medium with a gripping member that can be accommodated inside the recess; An image forming apparatus comprising:

Images