Image forming apparatus

Abstract

To hold a recording medium sent out from a sending unit with a circulating holding member.SOLUTION: An image forming apparatus 10 has: chains 49 that form part of a conveyance path A for conveying a sheet P; a gripper 42 that circulates while being fixed to the chains 49 and holds a leading end of the sheet P; an image forming unit 11 that forms an image on the sheet P at an image forming position 18 in the circulation path D of the chains 49; and a position adjustment unit 50 that sends out the sheet P to a delivery position D1 at which the gripper 42 holds the leading end of the sheet P. When a speed at which the gripper 42 is circulated by the chains 49 is a circulation speed Vg, the image forming apparatus decreases the conveyance speed of the sheet P from a first conveyance speed V1 faster than the circulation speed Vg to a second conveyance speed V2 slower than the first conveyance speed V1 just before the delivery position D1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Patent Document 1 discloses a technique related to a transfer paper conveyance device of a recording apparatus that forms a latent image by scanning a photosensitive drum in a spiral shape by moving a recording head having a light emitting element array and an imaging system in a substantially bus bar direction of the photosensitive drum rotating at a constant speed, and developing the latent image to transfer the obtained toner image onto transfer paper. In this prior art, a pair of endless chains or belts conveyed in a direction perpendicular to the axis of the photosensitive drum, gripper means for gripping and conveying the leading end of the transfer paper by pinning both ends to each of the pair of endless chains or belts, and means for variably controlling the mutual positional relationship in the conveyance direction of the pair of chains or belts are provided. The transfer paper is conveyed in an inclined state by inclining the direction of the gripper means by the same angle as the angle of the drum circumferential direction with respect to the main scanning direction of the spiral recording on the photosensitive member before conveying the transfer paper to the transfer position.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the conveyance speed of the recording medium when sent out by the sending unit is the same as the circumferential speed of the rotating holding member and enters the holding position at the same speed, it is impossible or difficult for the holding member to hold the recording medium.

[0005] It is an object to suppress poor holding of the recording medium by the rotating holding member as compared with the case where the recording medium sent out by the sending unit enters the holding position while maintaining a constant conveyance speed.

Means for Solving the Problem

[0006] A first aspect is an image forming apparatus including a rotating member forming part of a conveyance path for conveying a recording medium, a holding member fixed to the rotating member and rotating to hold a leading end portion of the recording medium, an image forming unit for forming an image on the recording medium at an image forming position in a rotation path of the rotating member, and a sending unit for sending out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium. When a rotation speed at which the holding member rotates by the rotating member is defined as a rotation speed Vg, the conveyance speed of the recording medium is decelerated from a first conveyance speed V1 faster than the rotation speed Vg before the holding position to a second conveyance speed V2 slower than the first conveyance speed V1.

[0007] In a second aspect, when a conveyance speed intermediate between the first conveyance speed V1 and the second conveyance speed V2 is defined as an intermediate conveyance speed Vc, the sending unit decelerates from the first conveyance speed V1 to the intermediate conveyance speed Vc, conveys the recording medium at the intermediate conveyance speed Vc, and then starts decelerating from the intermediate conveyance speed Vc to the second conveyance speed V2 at a preset timing. The image forming apparatus according to the first aspect.

[0008] A third aspect is the image forming apparatus according to the first aspect, which adjusts a timing at which the recording medium starts decelerating to the second conveyance speed V2 so that the leading end portion of the recording medium enters the holding position when the holding member moves to the holding position.

[0009] The fourth aspect is that the circumferential member is wound around the rotating member, and the holding member within the range where the circumferential member is wound around the rotating member holds the leading end portion of the recording medium at the holding position. The rotation period of the rotating member and the period of the intervals at which the plurality of holding members fixed to the circumferential member enter the holding position are made the same. When the time difference between the periodic signal detected for each rotation of the rotating member and the passing signal that detects that the leading end portion of the recording medium has passed through the passing position between the sending unit and the holding position is large as compared to when it is small, the timing at which the recording medium starts to decelerate to the second conveyance speed V2 is made faster. The image forming apparatus according to the third aspect.

[0010] The fifth aspect is the image forming apparatus according to the second aspect, which adjusts the timing at which the recording medium starts to decelerate to the intermediate conveyance speed Vc so that the leading end portion of the recording medium enters the holding position when the holding member moves to the holding position.

[0011] The sixth aspect is that the circumferential member is wound around the rotating member, and the holding member within the range where the circumferential member is wound around the rotating member holds the leading end portion of the recording medium at the holding position. The rotation period of the rotating member and the period of the intervals at which the plurality of holding members fixed to the circumferential member enter the holding position are made the same. When the time difference between the periodic signal detected for each rotation of the rotating member and the passing signal that detects that the leading end portion of the recording medium has passed through the passing position between the sending unit and the holding position is large as compared to when it is small, the timing at which the recording medium starts to decelerate to the intermediate conveyance speed Vc is made faster. The image forming apparatus according to the fifth aspect.

[0012] The seventh aspect is the image forming apparatus according to the fourth aspect or the sixth aspect, in which the circumferential member is a chain, the rotating member is a sprocket around which the chain is wound, and the number of teeth of the sprocket matches the number of pitches of the chain between the holding members fixed to the chain.

[0013] The eighth aspect is the image forming apparatus according to the first aspect, wherein the time from when the recording medium starts decelerating until it reaches the second conveyance speed V2 is constant.

[0014] The ninth aspect is the image forming apparatus according to the eighth aspect, wherein the time from when the recording medium starts decelerating until it reaches the second conveyance speed V2 is set so that deceleration is completed before the leading end portion of the recording medium enters the holding position.

[0015] The tenth aspect is the image forming apparatus according to any one of the first to ninth aspects, wherein deceleration to the second conveyance speed V2 is completed before the leading end portion of the recording medium enters the holding position.

[0016] The eleventh aspect is an image forming apparatus including: a circulating member that forms part of a conveyance path for conveying a recording medium; a holding member that is fixed to the circulating member and rotates to hold the leading end portion of the recording medium; an image forming unit that forms an image on the recording medium at an image forming position in a circulation path of the circulating member; and a sending unit that sends out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium, wherein the sending unit sends out the recording medium at a speed higher than the speed at which the holding member rotates by the circulating member, and the conveyance speed of the recording medium is decelerated after the leading end portion of the recording medium enters between the holding members.

Advantages of the Invention

[0017] According to the image forming apparatus of the first aspect, it is possible to suppress poor holding of the recording medium by the holding member as compared with the case where the recording medium sent out by the sending unit enters the holding position at a constant conveyance speed.

[0018] According to the image forming apparatus of the second aspect, it is possible to suppress poor holding of the recording medium by the holding member as compared with the case where the recording medium decelerates directly from the first conveyance speed V1 to the second conveyance speed V2.

[0019] According to the image forming apparatus of the third aspect, control is easier as compared with the case of adjusting the time during which the recording medium decelerates to the second conveyance speed V2.

[0020] According to the image forming apparatus of the fourth aspect, the timing at which the deceleration starts to the second conveyance speed V2 can be adjusted with high accuracy as compared with the case where only the passage signal is used.

[0021] According to the image forming apparatus of the fifth aspect, control is easier as compared with the case where the time during which the recording medium decelerates to the intermediate conveyance speed Vc is adjusted.

[0022] According to the image forming apparatus of the sixth aspect, the timing at which the deceleration starts to the intermediate conveyance speed Vc can be adjusted with high accuracy as compared with the case where only the passage signal is used.

[0023] According to the image forming apparatus of the seventh aspect, the rotation period of the rotating member can be made to coincide with the period of the interval at which the holding member enters the holding position.

[0024] According to the image forming apparatus of the eighth aspect, the timing at which the leading end portion of the recording medium enters the holding position is stabilized as compared with the case where the time from when the recording medium starts to decelerate until it reaches the second conveyance speed V2 is not constant.

[0025] According to the image forming apparatus of the ninth aspect, the holding of the leading end portion of the recording medium by the holding member is stabilized as compared with the case where the deceleration is completed after the leading end portion of the recording medium has entered the holding position.

[0026] According to the image forming apparatus of the tenth aspect, it is possible to suppress defective holding of the recording medium by the holding member as compared with the case where the deceleration to the second conveyance speed V2 is completed after entering the holding position.

[0027] According to the image forming apparatus of the eleventh aspect, it is possible to suppress defective holding of the recording medium by the holding member as compared with the case where the recording medium sent out by the sending unit enters the holding position at a constant conveyance speed.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0029] An example of an image forming apparatus according to an embodiment of the present invention will be described.

[0030] <First Embodiment> The image forming apparatus according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 10. Note that the arrow UP shown in each figure is in the vertical direction and indicates the upward direction of the apparatus. Also, as shown in FIG. 1, the arrow RH is in the horizontal direction and indicates the right side when facing the apparatus. Further, when the vertical direction is specified without any premise in the following description, it means the vertical direction of the apparatus shown in FIG. 1. Also, when the left and right directions are specified without any premise in the following description, it means the left (=L) and right (=R) directions when facing the apparatus shown in FIG. 1. Furthermore, when the depth direction (=front and back) is specified without any premise in the following description, it means the depth direction when facing the apparatus shown in FIG. 1.

[0031] [Overall Configuration of Image Forming Apparatus] First, the configuration of the image forming apparatus 10 will be described. FIG. 1 is a front view showing an outline of the image forming apparatus 10 according to the present embodiment.

[0032] As shown in FIG. 1, the image forming apparatus 10 includes a unit 10A arranged on the right side in the figure and a unit 10B arranged on the left side. The unit 10A arranged on the right side in FIG. 1 includes an image forming unit 11 that forms an image on a sheet P as an example of a recording medium.

[0033] The image forming unit 11 is provided with a droplet ejection mechanism 13 for forming an image by an inkjet method. The droplet ejection mechanism 13 includes droplet ejection heads 21Y, 21M, 21C, and 21K that eject ink droplets of each color as an example of droplets of black (K), yellow (Y), magenta (M), and cyan (C) onto a sheet P as an example of a recording medium.

[0034] The droplet ejection heads 21Y, 21M, 21C, and 21K are arranged in this order from the upstream side to the downstream side along the conveyance direction of the paper P, which will be described later. Also, the droplet ejection heads 21Y, 21M, 21C, and 21K are arranged such that the ejection surfaces 23Y, 23M, 23C, and 23K face the transfer body 36, which will be described later (see also FIG. 2). Note that the droplet ejection heads 21Y, 21M, 21C, and 21K are supplied with inks of respective colors from ink tanks (not shown).

[0035] Here, in the present embodiment, yellow (Y), magenta (M), cyan (C), and black (K) are the basic colors for outputting a color image. In the following description, when it is not necessary to distinguish each color, Y, M, C, and K after the reference numeral are omitted, and the droplet ejection head 21 is used.

[0036] The droplet ejection heads 21Y, 21M, 21C, and 21K for respective colors have basically the same structure except for the type of ink used. Also, the method of ejecting ink droplets from the droplet ejection head 21 is not particularly limited. For example, a thermal method, a piezoelectric method, or the like is used as a method of ejecting ink droplets.

[0037] As shown in FIG. 2, the droplet ejection heads 21Y, 21M, 21C, and 21K each have a length corresponding to the width of the image recording area on the paper P (see FIG. 1), and are full-line type heads in which a plurality of nozzles for ink ejection (not shown) are arranged on the ejection surfaces 23Y, 23M, 23C, and 23K over the entire width of the image recording area. Each droplet ejection head 21 is fixedly installed so as to extend in a direction orthogonal to the conveyance direction of the paper P (see FIG. 1).

[0038] In addition, in this embodiment, an example is given of a configuration in which an image is recorded using four colors of CMYK inks. However, the present invention is not limited to this, and the color of the ink and its combination may be changed. For example, light-colored inks such as light cyan and light magenta, dark inks, and special color inks may be added as necessary. Further, the arrangement order of the heads of each color is not limited to the illustrated order.

[0039] (Transfer body) As shown in FIGS. 1, 2, and 7, a transfer body 36 is provided in the image forming apparatus 10. The transfer body 36 has a cylindrical shape with an axial direction in the depth direction of the image forming apparatus 10 and is rotatably provided in the circumferential direction. A concave portion for accommodating a gripper 42 described later is formed on the outer periphery of the transfer body 36. Further, the transfer body 36 has sprockets around which chains 49 described later are wound at both axial ends.

[0040] (Image forming position) As shown in FIGS. 1 and 2 (also refer to FIG. 7), the image forming position 18 is a position where ink droplets are ejected from the ejection surface 23 (refer to FIG. 2) of each droplet ejection head 21 facing the transfer body 36 onto the paper P to form an image.

[0041] (Paper conveyance path) As shown in FIG. 1, the paper conveyance path A has a function of conveying the paper P supplied from the paper tray 38. The image forming apparatus 10 in this embodiment includes a plurality of paper trays 38. The paper P supplied from the paper tray 38 is conveyed along the paper conveyance path A. Then, it passes through the image forming position 18 and is discharged to the paper discharge tray 39.

[0042] More specifically, the paper conveyance path A is configured to pass through the units 10B, 10A, and 10B in this order. Thereby, the paper P conveyed along the paper conveyance path A is supplied from the paper tray 38 arranged in the unit 10B, passes through the unit 10A, and is further configured to be returned to the unit 10B.

[0043] On the other hand, the paper conveyance path A branches into a direction-changing path B for changing the conveyance direction of the paper on the downstream side of a receiving position D2 described later. This direction-changing path B is configured to merge into the paper conveyance path A on the downstream side in the conveyance direction. Note that the path in the paper conveyance path A between the direction-changing path B and the circulation path D is a merging path where the conveyance path on the front surface of the paper P and the conveyance path on the back surface merge. Note that the description of the circulation path D will be given later. Each conveyance path includes a plurality of paper conveyance rolls (not shown). By these rolls, the paper P is conveyed along each conveyance path.

[0044] (Image forming operation of the basic image) Next, an outline of the basic image forming operation on the paper P in the image forming apparatus 10 will be described.

[0045] Various operations in the image forming apparatus 10 are performed by a control unit 16 built into the apparatus. When the control unit 16 receives an image forming command from the outside, it operates the droplet ejection mechanism 13 of the image forming unit 11. Further, the control unit 16 sends the image data that has been subjected to image processing in an image signal processing unit (not shown) to the image forming unit 11. Then, ink droplets are ejected from each color droplet ejection head 21 onto the paper P at the image forming position 18, and an image is formed on the paper P.

[0046] During double-sided printing, the paper P that has passed through the receiving position D2 described later has its conveyance direction changed in the direction-changing path B provided in the conveyance path. Then, the paper P is conveyed through a conveyance path C including a plurality of rollers (not shown) and is conveyed back to the paper conveyance path A again.

[0047] (Gripper) As shown in FIGS. 3 and 4, the image forming apparatus 10 includes a gripper 42 as an example of a holding member that holds the leading end P1 of the conveyed paper P (see FIG. 3) and assists in the conveyance of the paper P. A plurality of clips 44 are provided across the depth direction of the apparatus (see FIG. 4).

[0048] The gripper 42 includes a clip 44, a rectangular case 46 covering the clip 44, and a shaft 48 extending in the depth direction. The clip 44 is fixed to the shaft 48 and is configured to be rotatable along with the circumferential rotation of the shaft 48.

[0049] The case 46 has a longitudinal direction in the depth direction and is held by the shaft 48. The case 46 is configured to rotate independently of the rotation of the clip 44. Further, the case 46 is configured to cover the upstream and downstream sides in the paper conveyance direction and the back surface direction of the paper with respect to the clip 44. Note that the "back surface" refers to the non-image forming surface of the paper P. In such a structure, the tip portion 45 of the clip 44 and the fixing claw portion 47 at the rear end of the case 46 are configured to be able to sandwich the tip portion P1 in the conveyance direction of the paper P. Note that the reference numeral 47A shown in FIG. 4 is the tip portion of the fixing claw portion 47.

[0050] (Chain) As shown in FIG. 3, both end portions of the shaft 48 in the depth direction are held by a conveyance chain 49 as an example of a circumferential member. By the circumrotation of the chain 49, the shaft 48 fixed to the chain 49 is also configured to circumrotate accordingly. Thereby, the gripper 42 is held by the chains 49 provided on the front side and the back side of the image forming apparatus 10 and circumrotates along a predetermined circumferential path D (see FIG. 1).

[0051] As shown in FIG. 7, the chain 49 is wound around a transfer member 36 and a sprocket 37 arranged at an interval in the depth direction, etc., and is configured to circumrotate along the circumferential path D by these.

[0052] (Circumferential path D) As shown in FIG. 1, the circulation path D is provided so as to partially overlap with the paper conveyance path A when viewed from the front of the image forming apparatus 10. Specifically, the circulation path D passes through the contact point with the paper conveyance path A on the outer periphery of the sprocket 37 provided below the transfer member 36 in the horizontal direction, and then overlaps with the paper conveyance path A until it passes through the receiving position D2 described later.

[0053] At the start point of the overlap between the paper conveyance path A and the circulation path D, the tip portion 45 of the clip 44 and the fixed claw portion 47 of the case 46 are close to each other, and the tip portion P1 of the paper P is clamped by the gripper 42. The holding start position of the paper P by the gripper 42 in the circulation path D is defined as the delivery position D1 where the paper P is delivered from the paper conveyance path A to the gripper.

[0054] Also, at the end point of the overlap between the circulation path D and the paper conveyance path A, the tip portion 45 of the clip 44 and the fixed claw portion 47 of the case 46 are separated from each other, and the tip portion P1 of the paper P is released. The release position of the paper P by the gripper 42 in the circulation path D is defined as the receiving position D2 where the paper P is received from the gripper 42 to the paper conveyance path A. Note that the delivery position D1 is arranged below the receiving position D2.

[0055] As shown in FIG. 1, in the present embodiment, when the paper P is delivered from the paper conveyance path A to the circulation path D, the paper P is delivered from the left side to the right side with respect to the image forming position. In other words, the paper feed direction at the delivery position D1 is conveyed from the left side direction to the right side direction.

[0056] On the other hand, when the paper P is received into the circulation path D, the paper P is received from the right side to the left side in the figure. In other words, the paper discharge direction at the receiving position D2 is conveyed from the right side direction to the left side direction.

[0057] At the receiving position D2 in the circulation path D, a conveyance cylinder 31 is provided. Sprockets around which a chain 49 described later is wound are provided at both axial ends of the conveyance cylinder 31.

[0058] (Position adjustment unit) As shown in FIG. 1, the position adjustment unit 50 is disposed in a merging path provided between the direction changing path B and the delivery position D1 in the paper conveyance path A.

[0059] As shown in FIG. 5, the position adjustment unit 50 includes conveyance rolls 51, 52, registration rolls 55 and passing sensors 62, 64, etc. Each roll is disposed above or below the paper conveyance path A. The upper conveyance roll 51 and the lower conveyance roll 52, and the upper registration roll 55 and the lower registration roll 56 rotate in pairs to convey the paper P.

[0060] Each of the passing sensors 62, 64 detects the passing and non-passing states of the paper P conveyed through the paper conveyance path A. The operations of the conveyance rolls 51, 52 and the registration rolls 55, 56 are appropriately controlled by the control unit 16 that receives signals from the passing sensors 62, 64.

[0061] (Operation in the position adjustment unit) As shown in FIG. 5, when the leading end P1 of the paper P (see FIG. 3) reaches the registration rolls 55, 56, the conveyance of the paper P stops momentarily, and the registration rolls 55, 56 are rotationally driven at a set timing, thereby being sent out to the delivery position D1. The timing of rotationally driving the registration rolls 55, 56 is controlled by detecting the passing timing of the leading end P1 of the paper P by the passing sensor 62.

[0062] (Delivery of the paper) As shown in FIGS. 6(A) to (C), the paper P that has passed through the position adjustment unit 50 is clamped on the circumference of the sprocket 37 in FIG. 5 by the fixed claw portion 47 of the case 46 and the tip portion 45 of the clip 44 in the gripper 42. The gripper 42 is supplied while moving along the circumferential path D in accordance with the conveyance timing of the leading end P1 of the paper P.

[0063] At this time, as shown in FIG. 6(A), the case 46 and the clip 44 are in an open state.

[0064] Also, as shown in FIG. 6(B), the gripper 42 is configured to gradually approach between the case 46 and the clip 44 while moving along the circumferential path D in accordance with the conveyance timing of the sheet P. Then, from the sheet conveyance path A, the tip 45 of the clip 44 lifts the tip P1 of the sheet P.

[0065] As shown in FIG. 6(C), the tip P1 of the sheet P is further lifted by the clip 44 and is transferred from the sheet conveyance path A to the circumferential path D in a state of being sandwiched between the fixed claw portion 47 of the case 46 and the tip 45 of the clip 44. Thereafter, the sheet P is conveyed along the circumferential path D by the gripper 42.

[0066] Note that the position where the sheet P is transferred from the sheet conveyance path A to the circumferential path D is defined as the transfer position D1.

[0067] (Inversion of the sheet) As shown in FIG. 1, after the sheet P is transferred to the circumferential path D, it is inverted front to back along the outer periphery of the transfer member 36. Then, the sheet P is conveyed to the image forming position 18 provided on the outer periphery of the transfer member 36. That is, in the process of inverting the sheet P along the circumferential path and the outer periphery of the transfer member 36, the secondary transfer position 20 is configured to pass through the secondary transfer position 20.

[0068] The surface of the sheet P facing the backup roll 33 when passing through the image forming position 18 is the image forming surface and is regarded as the front surface. In other words, at the position adjustment unit 50 and the transfer position D1, the sheet P is conveyed with the non-image forming surface, i.e., the back surface, facing upward.

[0069] (Receiving of the sheet) The sheet P is received from the circulation path D to the sheet conveyance path A. The branch point between this circulation path D and the sheet conveyance path A is set as the reception position D2. At the reception position D2, the gripper 42 holding the leading end portion P1 (see FIG. 3) of the sheet P is opened, whereby the sheet P is received from the circulation path D to the sheet conveyance path A.

[0070] [Configuration of the main part] Next, the configuration of the main part of this embodiment will be described.

[0071] The control unit 16 shown in FIG. 11 has a function of controlling the entire image forming apparatus 10. The hardware configuration of the control unit 16 is composed of a computer including a CPU (Central Processing Unit) not shown, a ROM (Read Only Memory) storing programs for realizing each processing routine, a RAM (Random Access Memory) for temporarily storing data, a memory as storage means, and a network interface.

[0072] The chain drive mechanism 79 shown in FIG. 11 is configured to drive the transfer body 36 around which the chain 49 is wound, the sprocket 37, etc. (see FIGS. 5 etc.) in a circular motion. The chain drive mechanism 79 has its circular motion speed etc. controlled by the control unit 16.

[0073] As shown in FIG. 5, at the passing position TS (see FIG. 9) between the registration rollers 55, 56 and the delivery position D1 in the sheet conveyance path A, a passing sensor 64 for detecting the leading end portion P1 (see FIG. 3) of the sheet P is provided. Note that a signal detected by the passing sensor 64 detecting the leading end portion P1 (see FIG. 3) of the sheet P at the passing position TS is defined as the passing signal KS.

[0074] The image forming apparatus 10 has a cycle sensor 202 for detecting the rotation cycle of the sprocket 37. The cycle sensor 202 detects the detection portion 204 provided on the sprocket 37 once per rotation. Note that a signal detected by the detection portion 204 each time the sprocket 37 makes one rotation by the cycle sensor 202 is defined as the cycle signal CS.

[0075] As shown in FIG. 11, the passing signal KS detected by the passing sensor 64 and the periodic signal SS detected by the periodic sensor 202 are sent to the control unit 16 (see also FIG. 1).

[0076] As shown in FIG. 10, the chain 49 has a structure in which roller links 59 assembled with bushes fitted with freely rotating rollers and link plates are connected by pin links 57.

[0077] A plurality of grippers 42 are fixed to the chain 49 at preset intervals. The number of spaces L1 between the grippers 42 fixed to the chain 49 matches the number of teeth L2, which is the total number of teeth 129 of the sprocket 37. Therefore, the entry cycle GS, which is the cycle in which the gripper 42 enters the delivery position D1, and the rotation cycle PS in which the sprocket 37 makes one rotation match. Note that the number of spaces L1 between the grippers 42 includes the number of roller links 59 to which the grippers 42 are fixed.

[0078] The position adjuster 50 shown in FIG. 5 can adjust the conveyance speed of the fed sheet P by adjusting the rotation speeds of the resist rollers 55, 56, etc. The conveyance speed of the sheet P by the position adjuster 50 is controlled by the control unit 16 (see FIG. 11). Also, it is controlled so that the conveyance speed of the sheet P is decelerated from the conveyance speed when the position adjuster 50 feeds out the sheet P and the leading end P1 of the sheet P (see FIG. 3) enters the delivery position D1.

[0079] Specifically, the circumferential speed of the gripper 42 is the circumferential speed Vg (m / s), the conveyance speed when the position adjuster 50 feeds out the sheet P is the first conveyance speed V1 (m / s), the conveyance speed of the sheet P at the delivery position D1 of the leading end P1 of the sheet P (see FIG. 3) is the second conveyance speed V2 (m / s), then V1 > Vg V1 > V2 V2 ≈ Vg It is controlled by the control unit 16 (see FIG. 11) so as to be in the relevant relationship.

[0080] V1 is set in the range of 1.02 times or more and 1.09 times or less of VG, and in this embodiment, V1 = VG × 1.05 is set. Also, V2 is set in the range of ±1% of Vg, and in this embodiment, V2 = Vg × 1.005 is set. Note that these setting ranges are just examples and are not limited thereto. They may be appropriately set according to specifications such as the circumferential speed. Also, at least "V1 > Vg" and "V1 > V2" need to be satisfied.

[0081] Also, the circumferential speed Vg (m / s) at which the gripper 42 rotates is the same as the rotational speed of the sprocket 37.

[0082] Furthermore, in this embodiment, the control unit 16 (see FIG. 11) adjusts the timing TA (see FIG. 9) at which deceleration starts to the second conveyance speed V2 so that the leading end P1 of the sheet P (see FIGS. 6 and 8) enters the delivery position D1 when the gripper 42 moves to the delivery position D1. Note that the timing when the deceleration to the second conveyance speed V2 is completed is defined as timing TB (see FIG. 9).

[0083] The time TC between the timing TA and the timing TB shown in FIG. 9 is controlled to be constant. Also, the timing TB when the deceleration to the second conveyance speed V2 is completed is set so as to be completed before the leading end P1 of the sheet P (see FIGS. 6 and 8) enters the delivery position D1.

[0084] Specifically, as shown in FIG. 8(A), the position adjustment unit 50 feeds out the sheet P at the first conveyance speed V1. As shown in FIG. 8(B), the control unit 116 controls the position adjustment unit 50 to start decelerating the sheet P to the second conveyance speed V2. As shown in FIG. 8(C), with the deceleration to the second conveyance speed V2 completed, the leading end P1 of the sheet P enters the delivery position D1. The delivery position D1 in this embodiment is a point W (mm) ahead along the conveyance direction from the leading end 47A of the fixed claw portion 47. Also, in this embodiment, W is 5 mm.

[0085] From another perspective, the position adjustment unit 50 feeds out the sheet P at a conveyance speed faster than the rotation speed at which the gripper 42 rotates, and after the leading end P1 of the sheet P enters the gripper 42, the conveyance speed of the sheet P is decelerated. Note that "entering the gripper 42" means that the sheet P enters between the case 46 and the clip 44 that constitute the gripper 42. More specifically, it is a state in which the virtual line connecting the tip of the case 46 and the tip of the clip 44 intersects the sheet P.

[0086] Then, as shown in FIGS. 8(D) to 8(F), the gripper 42 holds and conveys the leading end P1 of the sheet P.

[0087] In the present embodiment, the control unit 16 (see FIG. 11) uses the time difference t between the periodic signal SS of the sprocket 37 detected by the periodic sensor 202 (see FIG. 5) and the passing signal KS detected by the passing sensor 64 for the leading end P1 (see FIG. 3) of the sheet P at the passing position TS (see FIG. 5) to adjust the timing TA (see FIG. 8(B)) at which the deceleration to the second conveyance speed V2 starts.

[0088] Specifically, the control unit 16 (see FIG. 1) controls as follows

[0089] The reference value of the design time difference t is defined as the reference value t0, and the reference value of the timing at which the design deceleration starts is defined as the reference timing TD. Also, the difference between the periodic signal SS and the passing signal KS actually detected by the passing sensor 64 and the periodic sensor 202 is defined as the measured value t1, and the time from the reference value t0 is defined as Δt. Then, the control unit 16 (see FIG. 11) sets the timing TA based on the reference timing TD and Δt.

[0090] From another perspective, when the measured value t1 of the time difference t between the passing signal KS and the periodic signal SS is large, compared with the case where it is small, the timing TA at which the deceleration to the second conveyance speed V2 starts is advanced.

[0091] <Function> Next, the function of the present embodiment will be described.

[0092] The speed at which the gripper 42 rotates is the rotation speed Vg (m / s), The conveying speed when the position adjustment unit 50 sends out the paper P is the first conveying speed V1 (m / s), The conveying speed of the paper P at the delivery position D1 of the leading edge P1 of the paper P is a second conveying speed V2 (m / s), Then, V1>Vg V1>V2 The control unit 16 controls the relationship to be as follows:

[0093] From another perspective, the position adjustment unit 50 feeds out the paper P at a transport speed faster than the rotation speed of the gripper 42, and is controlled by the control unit 16 to slow down the transport speed of the paper P after the leading edge P1 of the paper P enters the gripper 42.

[0094] Therefore, compared to when the leading edge P1 of the paper sheet P sent out by the position adjustment unit 50 enters the delivery position D1 at a constant transport speed, it is possible to prevent the gripper 42 from improperly holding the leading edge P1 of the paper sheet P.

[0095] Here, the above will be explained in detail. As a first comparative example, consider a case where the leading edge P1 of the sheet P enters the delivery position D1 while maintaining the first conveying speed V1 when the position adjustment unit 50 sends out the sheet P. In this case, the conveying speed of the sheet P at the delivery position D1 is faster than the rotation speed Vg of the gripper 42, so the gripper 42 is likely to fail to hold the leading edge P1 of the sheet P properly.

[0096] As a second comparative example, consider a case where the position adjustment unit 50 feeds out the sheet P at the second conveyance speed V2, and the leading edge P1 enters the delivery position D1 at that conveyance speed. In this case, the conveyance speed of the sheet P when the position adjustment unit 50 feeds out the sheet P is approximately the same as the rotation speed of the gripper 42. Therefore, the leading edge P1 of the sheet P does not catch up with the gripper 42, and the gripper 42 is unable to hold the leading edge P1, or it is difficult to hold the leading edge P1, which is likely to result in poor holding.

[0097] In contrast, when the position adjustment unit 50 feeds out the sheet P as in the present embodiment, the first conveyance speed V1 is made faster than the rotation speed Vg at which the gripper 42 rotates, and then decelerated so that the second conveyance speed V2 of the sheet P at the delivery position D1 of the leading end P1 of the sheet P is the same speed or substantially the same speed as the rotation speed Vg. As a result, the gripper 42 can easily hold the leading end P1 of the sheet P, and the occurrence of poor holding is suppressed.

[0098] Further, in the present embodiment, the timing at which the sheet P starts to decelerate to the second conveyance speed V2 is adjusted so that the leading end P1 of the sheet P enters the delivery position D1 when the gripper 42 moves to the delivery position D1.

[0099] Therefore, by adjusting the length of the time from the first conveyance speed V1 to the second conveyance speed V2 of the sheet P, that is, the time TC between the timing TA and the timing TB, compared with the case where the leading end P1 of the sheet P enters the delivery position D1 when the gripper 42 moves to the delivery position D1, the control by the control unit 16 is easier.

[0100] Further, in the present embodiment, the rotation period PS of the sprocket 37 for one rotation and the entry period GS which is the period when the gripper 42 enters the delivery position D1 match. Therefore, using the period signal SS of the sprocket 37 detected by the period sensor 202, the timing at which the gripper 42 enters the delivery position D1 can be estimated with high accuracy.

[0101] Then, using the period signal SS of the sprocket 37 detected by the period sensor 202 and the passing signal KS in which the passing sensor 64 detects the leading end P1 of the sheet P at the passing position TS, the timing TA at which the sheet P starts to decelerate to the second conveyance speed V2 is adjusted. Therefore, for example, compared with the case of using only the passing signal KS, the timing TA at which the deceleration starts to the second conveyance speed V2 can be adjusted with high accuracy.

[0102] Further, in the present embodiment, by making the number of sheets L1 between the grippers 42 fixed to the chain 49 equal to the number of teeth L2 which is the total number of teeth 129 of the sprocket 37, the rotation period PS in which the sprocket 37 makes one rotation and the entry period GS which is the period in which the gripper 42 enters the delivery position D1 can be made to coincide with each other.

[0103] Further, in the present embodiment, the time from when the sheet P reaches the second conveyance speed V2 from the first conveyance speed V1, that is, the time TC between the timings TA and TB is constant. Therefore, compared with the case where the time TC is not constant, the timing at which the leading end P1 of the sheet P enters the delivery position D1 is stabilized.

[0104] Further, in the present embodiment, the deceleration to the second conveyance speed V2 is completed before the leading end P1 of the sheet P enters the delivery position D1. Therefore, compared with the case where the deceleration to the second conveyance speed V2 is completed after the leading end P1 of the sheet P enters the delivery position D1, the holding of the leading end P1 of the sheet P by the gripper 42 is stabilized.

[0105] <Second Embodiment> An image forming apparatus according to a second embodiment of the present invention will be described. Note that since only the [configuration of the main part] is different from the image forming apparatus of the first embodiment, only the [configuration of the main part] will be described. Also, overlapping descriptions will be omitted or simplified, and the same members and the like will be given the same reference numerals.

[0106] [Configuration of the Main Part] Next, the configuration of the main part of the present embodiment will be described.

[0107] The speed at which the gripper 42 orbits is the orbiting speed Vg (m / s), The conveyance speed when the position adjuster 50 feeds out the sheet P is the first conveyance speed V1 (m / s), The conveyance speed of the sheet P at the delivery position D1 of the leading end P1 (see FIG. 3) of the sheet P is the second conveyance speed V2 (m / s), The intermediate conveyance speed between the first conveyance speed V1 (m / s) and the second conveyance speed V2 (m / s) is the intermediate conveyance speed Vc (m / s), Then, V1 > Vc > Vg V1 > Vc > V2 V2 ≈ Vg It is controlled by the control unit 16 (see FIG. 11) so as to have the relationship of.

[0108] Also, V1 is set in the range of 1.02 times or more and 1.09 times or less of VG, and in this embodiment, V1 = VG × 1.05 is set. Also, V2 is set in the range of ±1% of Vg, and in this embodiment, V2 = Vg × 1.005 is set. Also, in this embodiment, Vc = (V1 + V2) / 2 is set. Note that these setting ranges are examples and are not limited thereto. They may be appropriately set according to specifications such as the circumferential speed. Also, at least "V1 > Vc > Vg" and "V1 > Vc > V2" need to be satisfied.

[0109] Note that the circumferential speed Vg (m / s) at which the gripper 42 rotates is the same as the rotational speed of the sprocket 37.

[0110] Then, as shown in FIG. 14, the control unit 16 (see FIG. 11) decelerates the conveyance speed of the sheet P from the first conveyance speed V1 to the intermediate conveyance speed Vc when the position adjustment unit 50 feeds out the sheet P, and then decelerates it to the second conveyance speed V2 so that the leading end P1 of the sheet P (see FIG. 3) enters the delivery position D1.

[0111] The deceleration from the intermediate conveyance speed Vc to the second conveyance speed V2 starts at a predetermined timing TQ. The timing TQ is in front of CW from the delivery position D1, and in this embodiment, CW is 10 mm.

[0112] Also, in this embodiment, the control unit 16 (see FIG. 11) adjusts the timing TP at which the deceleration starts to the intermediate conveyance speed Vc so that the leading end P1 of the sheet P (see FIGS. 6 and 8) enters the delivery position D1.

[0113] Note that the timing TR when the deceleration from the intermediate conveyance speed Vc to the second conveyance speed V2 is completed is set so as to be completed before the leading end P1 of the sheet P (see FIGS. 6 and 8) enters the delivery position D1.

[0114] Specifically, as shown in FIG. 13(A), the position adjustment unit 50 feeds out the sheet P at the first conveyance speed V1. As shown in FIG. 13(B), the control unit 16 controls the position adjustment unit 50 to decelerate the conveyance speed of the sheet P to the intermediate conveyance speed Vc and convey the sheet P at the intermediate conveyance speed Vc. As shown in FIG. 13(C), at a predetermined timing TR (see FIG. 14), the speed is decelerated from the intermediate conveyance speed Vc to the second conveyance speed V2, and the leading end P1 of the sheet P is made to enter the delivery position D1 in a state where the deceleration to the second conveyance speed V2 is completed. Note that the delivery position D1 in the present embodiment is a point W (mm) ahead from the leading end 47A of the fixed claw portion 47 along the conveyance direction. In the present embodiment, W is 5 mm. Then, as shown in FIGS. 13(D) to 13(F), the gripper 42 holds and conveys the leading end P1 of the sheet P.

[0115] In the present embodiment, the control unit 16 (see FIG. 11) adjusts the timing TP (see FIG. 14) at which the deceleration to the intermediate conveyance speed Vc starts, using the time difference t between the periodic signal SS of the sprocket 37 detected by the periodic sensor 202 (see FIG. 5) and the passing signal KS detected by the passing sensor 64 for the leading end P1 of the sheet P (see FIG. 3) at the passing position TS (see FIG. 5).

[0116] Specifically, the control unit 16 (see FIG. 1) controls as follows

[0117] Taking the reference value of the design time difference t as the reference value t0 and the reference value of the timing at which the design deceleration starts as the reference timing TD. Also, taking the difference between the periodic signal SS and the passing signal KS actually detected by the passing sensor 64 and the periodic sensor 202 as the measured value t1 and the time from the reference value t0 as Δt. Then, the control unit 16 (see FIG. 11) sets the timing TP (see FIG. 14) based on the reference timing TD and Δt.

[0118] From another perspective, when the measured value t2 of the time difference t between the passing signal KS and the periodic signal SS is large, compared with the case where it is small, the timing TP at which deceleration starts for the intermediate conveyance speed Vc is advanced.

[0119] <Function> Next, the function of this embodiment will be described.

[0120] Let the speed at which the gripper 42 rotates be the rotation speed Vg (m / s), let the conveyance speed when the position adjustment unit 50 feeds out the sheet P be the first conveyance speed V1 (m / s), let the conveyance speed of the sheet P at the delivery position D1 of the leading end P1 of the sheet P (see FIG. 3) be the second conveyance speed V2 (m / s), let the intermediate conveyance speed until deceleration is completed for the first conveyance speed V1 (m / s) and the second conveyance speed V2 (m / s) be the intermediate conveyance speed Vc (m / s), then, V1 > Vc > Vg V1 > Vc > V2 It is controlled by the control unit 16 so as to have the relationship.

[0121] And the control unit 16 decelerates the conveyance speed of the sheet P from the first conveyance speed V1 to the intermediate conveyance speed Vc and conveys it, and then decelerates it to the second conveyance speed V2 so that the leading end P1 of the sheet P enters the delivery position D1.

[0122] Therefore, compared with the case where the leading end P1 of the sheet P fed out by the position adjustment unit 50 enters the delivery position D1 at a constant conveyance speed, it is possible to suppress poor holding of the leading end P1 of the sheet P by the gripper 42.

[0123] Furthermore, compared with the case of directly decelerating from the first conveyance speed V1 to the second conveyance speed V2, the accuracy at which the leading end P1 of the sheet P enters the delivery position D1 in the state of decelerating to the second conveyance speed V2 is improved, so that poor holding of the leading end P1 of the sheet P by the gripper 42 can be further suppressed.

[0124] Further, in the present embodiment, the timing at which the paper P starts to decelerate to the intermediate conveyance speed Vc is adjusted so that the leading end P1 of the paper P enters the delivery position D1 when the gripper 42 moves to the delivery position D1. Therefore, by adjusting the length of the time from the first conveyance speed V1 to the intermediate conveyance speed Vc, compared with the case where the leading end P1 of the paper P enters the delivery position D1 when the gripper 42 moves to the delivery position D1, the control by the control unit 16 is facilitated.

[0125] Further, in the present embodiment, the rotation period PS during which the sprocket 37 makes one rotation and the entry period GS which is the period during which the gripper 42 enters the delivery position D1 match. Therefore, using the period signal SS of the sprocket 37 detected by the period sensor 202, the timing at which the gripper 42 enters the delivery position D1 can be estimated with high accuracy.

[0126] Then, using the period signal SS of the sprocket 37 detected by the period sensor 202 and the passage signal KS in which the passage sensor 64 detects the leading end P1 of the paper P at the passage position TS, the timing TQ at which the paper P starts to decelerate to the intermediate conveyance speed Vc is adjusted. Therefore, for example, compared with the case of using only the passage signal KS, the timing TQ at which the deceleration to the intermediate conveyance speed Vc starts can be adjusted with high accuracy.

[0127] Further, in the present embodiment, by making the number of frames L1 between the grippers 42 fixed to the chain 49 and the total number of teeth L2 of the teeth 129 of the sprocket 37 the same, the rotation period PS during which the sprocket 37 makes one rotation and the entry period GS which is the period during which the gripper 42 enters the delivery position D1 can be made to match.

[0128] Further, in the present embodiment, the deceleration to the second conveyance speed V2 is completed before the leading end P1 of the paper P enters the delivery position D1. Therefore, compared with the case where the deceleration to the second conveyance speed V2 is completed after the leading end P1 of the paper P enters the delivery position D1, the holding of the leading end P1 of the paper P by the gripper 42 is stabilized.

[0129] [Modification Example] Next, a modification of the second embodiment will be described.

[0130] In the above embodiment, the timing TQ for starting the deceleration from the intermediate conveyance speed Vc to the second conveyance speed V2 shown in FIG. 14 was constant. However, the control unit 16 (see FIG. 11) in the modification adjusts the timing TQ according to the paper quality of the paper P.

[0131] Specifically, when the paper P is weak, the leading end P1 of the paper P may bend, and the entry of the leading end P1 into the delivery position D1 may be delayed. Therefore, it is necessary to delay the timing TQ accordingly.

[0132] Therefore, in this modification, the timing TQ is adjusted according to the paper quality of the paper P. That is, when the paper thickness of the paper P is thin and the paper is weak, the timing TQ is delayed more than when the paper thickness is thick and the paper is strong.

[0133] Specifically, the control unit 16 stores the timing TQ corresponding to the paper quality of the paper P, and starts decelerating to the intermediate conveyance speed Vc at the stored timing TQ. The paper quality of the paper P may be detected by a sensor or input by the user from an operation panel or the like.

[0134] In this way, since the control unit 16 (see FIG. 11) adjusts the timing TQ according to the paper quality of the paper P, it is possible to further suppress the poor holding of the leading end P1 of the paper P by the gripper 42 as compared with the case where the timing TQ is constant.

[0135] Note that the "stiffness" of the paper P is the resistance when a bending force is applied to the paper. From another perspective, the "stiffness" of the paper P can be referred to as the rigidity of the paper.

[0136] <Other examples of the image forming unit> Next, other examples of the image forming unit of the image forming apparatus in the first embodiment and the second embodiment will be described.

[0137] The image forming unit 99 shown in FIG. 12 includes an image forming unit 12, which will be described later, for forming an image by an electrophotographic method, an intermediate transfer belt 22 for holding the formed image, and an intermediate transfer unit 14 for mounting and supporting the intermediate transfer belt 22. Further, in the image forming apparatus 10, a transfer member 36 for transferring the image from the intermediate transfer unit 14 to a sheet P for image recording is provided on the lower left side of the intermediate transfer unit 14.

[0138] The contact portion between the intermediate transfer belt 22 and the transfer member 36 is a secondary transfer position 20, which is an example of an image forming position. At this secondary transfer position 20, the toner image formed by the image forming unit 12 is transferred to the surface of the sheet P via the intermediate transfer belt 22 mounted on the intermediate transfer unit 14.

[0139] The image forming unit 99 is provided with a plurality of image forming units 12 for forming toner layers of respective colors. In the present embodiment, a total of four image forming units 12 corresponding to the respective colors of a yellow image forming unit 12Y, a magenta image forming unit 12M, a cyan image forming unit 12C, and a black image forming unit 12K are provided.

[0140] Note that yellow (Y), magenta (M), cyan (C), and black (K) are basic colors for outputting a color image. In the following description, when it is not necessary to distinguish each color in each image forming unit 12, it may be simply referred to as the "image forming unit 12", and the symbols Y, M, C, or K meaning the image forming units corresponding to the respective colors may be appropriately omitted in the description.

[0141] The color image forming units 12 are basically configured in the same manner except for the type of toner used. Each image forming unit 12 is provided with a rotating cylindrical photoreceptor 24 and a charger 26 for charging the photoreceptor 24. Further, the image forming unit 12 is provided with an exposure device 28 for irradiating the charged photoreceptor 24 with exposure light to form an electrostatic latent image, and a developing device 30 for developing the electrostatic latent image as an image formed by a toner layer with a developer containing toner. Further, a cleaner 29 is provided for removing the toner remaining on the surface of the photoreceptor 24 after the toner is transferred from the photoreceptor 24 to the intermediate transfer belt 22.

[0142] The photoreceptors 24 of each color are configured to be able to contact the outer peripheral surface of the intermediate transfer belt 22. Also, in the circumferential direction of the intermediate transfer belt 22, the respective image forming units 12 corresponding to yellow, magenta, cyan, and black are arranged side by side along the upstream side to the downstream side.

[0143] (Intermediate Transfer Unit) The intermediate transfer unit 14 includes a primary transfer roll 34 arranged to face the color image forming units 12 and a backup roll 33 arranged to face the transfer member 36.

[0144] (Intermediate Transfer Belt) The intermediate transfer belt 22 is formed in an endless shape. Also, the intermediate transfer belt 22 is wound around a plurality of rolls 32 to determine its posture. In the present embodiment, the posture of the intermediate transfer belt 22 is a substantially obtuse triangle shape that is long in the apparatus width direction and has an obtuse convex portion downward in a front view. Among the plurality of rolls 32, one roll (not shown) has a function of rotating the intermediate transfer belt 22 in the direction of arrow X by the power of a motor (not shown). The intermediate transfer belt 22 rotates in the direction of arrow X to convey the primarily transferred image to the secondary transfer position 20.

[0145] The intermediate transfer belt 22 is configured to be able to rotate in the direction of arrow X while being in contact with or separated from the photoreceptors 24 of each color.

[0146] (Primary transfer) Each primary transfer unit 19 is constituted by the contact portions of the photoreceptor 24, the intermediate transfer belt 22, and the primary transfer roll 34. The primary transfer roll 34 is disposed to face the photoreceptor 24 with the intermediate transfer belt 22 interposed therebetween. The primary transfer roll 34 and the intermediate transfer belt 22 are configured to contact each other with a predetermined load.

[0147] Also, a voltage is applied to the primary transfer roll 34 by a power supply unit (not shown). This voltage is the primary transfer voltage for the toner image formed on the photoreceptor 24 to be primarily transferred to the intermediate transfer belt 22 between the photoreceptor 24 and the primary transfer roll 34.

[0148] (Transfer member) A transfer member 36 is provided at a position facing the backup roll 33 with the intermediate transfer belt 22 interposed therebetween. The transfer member 36 has a cylindrical shape with an axial direction in the depth direction of the image forming apparatus 10 and is rotatably provided in the circumferential direction.

[0149] A voltage is applied to the transfer member 36 by a power supply unit (not shown). This voltage is the secondary transfer voltage when the toner image transferred while being superimposed on the intermediate transfer belt 22 is secondarily transferred to the sheet P conveyed to the secondary transfer position 20.

[0150] (Secondary transfer) The secondary transfer position 20 is constituted by the contact portion between the intermediate transfer belt 22 and the transfer member 36 formed in a roll shape. The intermediate transfer belt 22 is configured to contact the transfer member 36 with a predetermined load by the backup roll 33 disposed to face the transfer member 36.

[0151] (Fixing device) The fixing device 40 is disposed on the downstream side of the secondary transfer position 20 in the paper P conveyance direction. This fixing device 40 includes the opposing conveyance cylinder 31 and the heating roll 43. The conveyance cylinder 31 and the heating roll 43 are installed so as to oppose each other with the aforementioned paper conveyance path A interposed therebetween. That is, the paper P to be fixed is conveyed so as to pass between the conveyance cylinder 31 and the heating roll 43.

[0152] (Image forming operation of the basic image) Next, an outline of the basic image forming operation on the paper P in the image forming unit 99 will be described.

[0153] When the control unit 16 receives an image forming command from the outside, it operates each image forming unit 12. Each photosensitive drum 24 is charged by the charger 26 while rotating. Further, the control unit 16 sends the image data subjected to image processing in an image signal processing unit (not shown) to each exposure device 28. Each exposure device 28 exposes each charged photosensitive drum 24 by irradiating exposure light to each photosensitive drum 24 according to the image data. Thereby, an electrostatic latent image is formed on the outer peripheral surface of each photosensitive drum 24. The electrostatic latent image formed on each photosensitive drum 24 is developed by each developing device 30, and a toner image of each color is formed on the photosensitive drum 24 corresponding to each color.

[0154] The toner images of each color formed on each photosensitive drum 24 are primarily transferred to the intermediate transfer belt 22 by the primary transfer roll 34 of each color in each primary transfer unit. At this time, as the intermediate transfer belt 22 rotates, the toner images of each color are sequentially primarily transferred to the intermediate transfer belt 22 while being superimposed. The toner images superimposed in this way are conveyed to the secondary transfer position 20 by the rotation of the intermediate transfer belt 22. Then, the superimposed toner images are transferred from the intermediate transfer belt 22 to the paper P at the secondary transfer position 20.

[0155] The sheet P onto which the toner image has been secondarily transferred is conveyed toward the fixing device 40. In the fixing device 40, the sheet P is heated and pressed against the fixing roll respectively. Thereby, the toner images formed by the respective image forming units 12 are fixed onto the sheet P.

[0156] During double-sided printing, the sheet P that has passed through the fixing device 40 has its conveyance direction changed in the direction-changing path B provided in the conveyance path. Then, the sheet P is conveyed through a conveyance path C configured to include a plurality of rollers (not shown) and is conveyed back to the sheet conveyance path A.

[0157] <Others> Note that the present invention is not limited to the above-described embodiment.

[0158] For example, in the above-described embodiment, the conveyance speed when the position adjustment unit 50 sends out the sheet P is set as the first conveyance speed V1 (m / s), but it is not limited thereto. The conveyance speed when the position adjustment unit 50 sends out the sheet P may be set as a third conveyance speed V3 that is faster or slower than the first conveyance speed V1 (m / s), and then the conveyance speed may be changed from the third conveyance speed V3 to the first conveyance speed V1 (m / s).

[0159] When the third conveyance speed V3 is slower than the first conveyance speed V1 (m / s), the magnitude relationship between the third conveyance speed V3 and the circumferential speed Vg (m / s) at which the gripper 42 rotates is not specified. That is, any of V3 > Vg, V3 = Vg, and V3 < Vg may be possible.

[0160] Also, when the third conveyance speed V3 is slower than the first conveyance speed V1 (m / s), the magnitude relationship between the third conveyance speed V3 and the second conveyance speed is not specified. That is, any of V3 > V2, V3 = V2, and V3 < V2 may be possible.

[0161] Further, for example, in the above embodiment, the timing TA at which the sheet P starts to decelerate to the second conveyance speed V2 or the timing TQ at which the sheet P starts to decelerate to the intermediate conveyance speed Vc is adjusted using the periodic signal SS of the sprocket 37 detected by the periodic sensor 202 and the passage signal KS detected by the passage sensor 64 detecting the leading end P1 of the sheet P at the passage position TS. However, the present invention is not limited to this. The timing TA at which the sheet P starts to decelerate to the second conveyance speed V2 or the timing TQ at which the sheet P starts to decelerate to the intermediate conveyance speed Vc may be adjusted using other signals.

[0162] Further, for example, in the above embodiment, when the gripper 42 moves to the delivery position D1, the timing at which the sheet P starts to decelerate to the second conveyance speed V2 or the timing TQ at which the sheet P starts to decelerate to the intermediate conveyance speed Vc is adjusted so that the leading end P1 of the sheet P enters the delivery position D1. However, the present invention is not limited to this. The timing TA at which the sheet P starts to decelerate to the second conveyance speed V2 or the timing TQ at which the sheet P starts to decelerate to the intermediate conveyance speed Vc may be fixed.

[0163] Further, for example, in the electrophotographic image forming unit 99 of the above embodiment, the toner image held by the intermediate transfer belt 22 as an example of the image holding member and the intermediate transfer member is transferred to the sheet P. However, the present invention is not limited to this. The image forming apparatus may be configured to transfer the toner image held by the photoreceptor as an example of the image holding member to the recording medium.

[0164] Further, for example, in the above embodiment, the image forming method of the image forming unit is the inkjet method or the electrophotographic method. However, the present invention is not limited to these. The image forming unit may be an image forming method other than these, for example, the offset printing method.

[0165] Further, for example, in the above embodiment, the gripper 42 as an example of the holding member is exemplified as having a configuration for physically holding the leading end P1 of the sheet P. However, the present invention is not limited to such a structure, and for example, the leading end of the sheet P may be held by the force of sucking air.

[0166] Also, for example, in the above embodiment, the circulating member was a chain, but it is not limited to this. For example, the circulating member may be a belt.

[0167] Also, the configuration of the image forming apparatus is not limited to the configuration of the above embodiment and can be various configurations. Furthermore, it can be implemented in various modes without departing from the gist of the present invention.

Explanation of Reference Numerals

[0168] 10 Image forming apparatus 11 Image forming unit 18 Image forming position 20 Secondary transfer position (an example of the image forming position) 37 Sprocket (an example of the rotating member) 42 Gripper (an example of the holding member) 49 Chain (an example of the circulating member) 50 Position adjusting unit (an example of the feeding unit) 99 Image forming unit P Paper (an example of the recording medium) P1 Leading end A Paper conveyance path D Circulating path D1 Delivery position (an example of the holding position)

Claims

1. A rotating member forming part of a conveyance path for conveying a recording medium, a holding member fixed to the rotating member and rotating to hold a leading end portion of the recording medium, an image forming unit that forms an image on the recording medium at an image forming position in a rotation path of the rotating member, a feeding unit that feeds out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium, characterized in that when a rotation speed of the holding member rotated by the rotating member is defined as a rotation speed Vg, a conveyance speed of the recording medium is decelerated from a first conveyance speed V1, which is faster than the rotation speed Vg before the holding position, to a second conveyance speed V2, which is slower than the first conveyance speed V1 and is the same as or substantially the same as the rotation speed Vg, an image forming apparatus.

2. When an intermediate conveyance speed Vc is defined as a conveyance speed intermediate between the first conveyance speed V1 and the second conveyance speed V2, the feeding unit decelerates from the first conveyance speed V1 to the intermediate conveyance speed Vc, conveys the recording medium at the intermediate conveyance speed Vc, and then starts decelerating from the intermediate conveyance speed Vc to the second conveyance speed V2 at a preset timing. The image forming apparatus according to claim 1.

3. Adjusting a timing at which the recording medium starts decelerating to the second conveyance speed V2 so that a leading end portion of the recording medium enters the holding position when the holding member moves to the holding position. The image forming apparatus according to claim 1.

4. The rotating member is wound around a rotary member, the holding member within a range where the rotating member is wound around the rotary member holds the leading end portion of the recording medium at the holding position, a rotation period of the rotary member and a period of an interval at which a plurality of the holding members fixed to the rotating member enter the holding position are the same, when a time difference between a periodic signal detected every rotation of the rotary member and a passing signal for detecting that a leading end portion of the recording medium has passed through a passing position between the feeding unit and the holding position is large, compared with a case where the time difference is small, the timing at which the recording medium starts decelerating to the second conveyance speed V2 is made faster. The image forming apparatus according to claim 3.

5. Adjusting a timing at which the recording medium starts decelerating to the intermediate conveyance speed Vc so that a leading end portion of the recording medium enters the holding position when the holding member moves to the holding position. The image forming apparatus according to claim 2.

6. The rotating member is wound around a rotary member, The holding member within the range where the circumferential member is wound around the rotating member holds the leading end portion of the recording medium at the holding position, the rotation period of the rotating member and the period of the intervals at which the plurality of holding members fixed to the circumferential member enter the holding position are made the same, when the time difference between the periodic signal detected each time the rotating member rotates and the passing signal for detecting that the leading end portion of the recording medium has passed through the passing position between the sending portion and the holding position is large, compared to when it is small, the timing at which the recording medium starts to decelerate to the intermediate conveyance speed Vc is made faster, The image forming apparatus according to claim 5.

7. The circumferential member is a chain, the rotating member is a sprocket around which the chain is wound, the number of teeth of the sprocket and the number of pitches of the chain between the holding members fixed to the chain match each other, The image forming apparatus according to claim 4 or claim 6.

8. The time from when the recording medium starts to decelerate until it reaches the second conveyance speed V2 is made constant, The image forming apparatus according to claim 1.

9. The time from when the recording medium starts to decelerate until it reaches the second conveyance speed V2 is set so that the deceleration is completed before the leading end portion of the recording medium enters the holding position, The image forming apparatus according to claim 8.

10. The deceleration to the second conveyance speed V2 is completed before the leading end portion of the recording medium enters the holding position, The image forming apparatus according to any one of claims 1 to 9.

11. A circumferential member forming part of a conveyance path for conveying a recording medium, a holding member fixed to the circumferential member and rotating to hold the leading end portion of the recording medium, an image forming unit that forms an image on the recording medium at an image forming position in the circumferential path of the circumferential member, a sending unit that sends out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium, having, the sending unit sends out the recording medium at a speed faster than the speed at which the holding member rotates by the circumferential member, after the leading end portion of the recording medium enters between the holding members, the conveyance speed of the recording medium is decelerated to the same speed or substantially the same speed as the speed at which the holding member rotates, An image forming apparatus.

12. A circumferential member forming part of a conveyance path for conveying a recording medium, a holding member fixed to the circumferential member and rotating to hold the leading end portion of the recording medium, At an image forming position in the circulation path of the circumferential member, an image forming unit that forms an image on the recording medium; A feeding unit that feeds out the recording medium to a holding position where the holding member holds the leading end of the recording medium; It has: When the speed at which the holding member circulates by the circumferential member is defined as the circulation speed Vg, The conveyance speed of the recording medium is decelerated from a first conveyance speed V1, which is faster than the circulation speed Vg, in front of the holding position, to a second conveyance speed V2, which is slower than the first conveyance speed V1. The timing at which the recording medium starts to decelerate to the second conveyance speed V2 is adjusted so that when the holding member moves to the holding position, the leading end of the recording medium enters the holding position. The circumferential member is wound around a rotating member. The holding member within the range where the circumferential member is wound around the rotating member holds the leading end of the recording medium at the holding position. The rotation period of the rotating member and the period of the intervals at which the plurality of holding members fixed to the circumferential member enter the holding position are made the same. When the time difference between the periodic signal detected each time the rotating member rotates and the passing signal that detects that the leading end of the recording medium has passed through the passing position between the feeding unit and the holding position is large, compared with the case when it is small, the timing at which the recording medium starts to decelerate to the second conveyance speed V2 is made faster. An image forming apparatus.

13. A circumferential member that forms part of a conveyance path for conveying a recording medium; A holding member that is fixed to the circumferential member and circulates, holding the leading end of the recording medium; At an image forming position in the circulation path of the circumferential member, an image forming unit that forms an image on the recording medium; A feeding unit that feeds out the recording medium to a holding position where the holding member holds the leading end of the recording medium; It has: When the speed at which the holding member circulates by the circumferential member is defined as the circulation speed Vg, The conveyance speed of the recording medium is decelerated from a first conveyance speed V1, which is faster than the circulation speed Vg, in front of the holding position, to a second conveyance speed V2, which is slower than the first conveyance speed V1. When an intermediate conveyance speed between the first conveyance speed V1 and the second conveyance speed V2 is defined as the intermediate conveyance speed Vc, The feeding unit decelerates from the first conveyance speed V1 to the intermediate conveyance speed Vc and conveys the recording medium at the intermediate conveyance speed Vc, and then starts to decelerate from the intermediate conveyance speed Vc to the second conveyance speed V2 at a preset timing. When the holding member moves to the holding position, the timing at which the recording medium starts to decelerate to the intermediate conveyance speed Vc is adjusted so that the leading end portion of the recording medium enters the holding position. An image forming apparatus.

14. The circumferential member is wound around a rotating member. The holding member within the range where the circumferential member is wound around the rotating member holds the leading end portion of the recording medium at the holding position. The rotation period of the rotating member and the period of the intervals at which a plurality of the holding members fixed to the circumferential member enter the holding position are made the same. When the time difference between the periodic signal detected each time the rotating member rotates and the passing signal that detects that the leading end portion of the recording medium has passed through the passing position between the sending portion and the holding position is large, compared to when it is small, the recording medium starts to decelerate to the intermediate conveyance speed Vc To speed up the timing. The image forming apparatus according to claim 13.

15. The circumferential member is a chain. The rotating member is a sprocket around which the chain is wound. The number of teeth of the sprocket and the number of pitches of the chain between the holding members fixed to the chain match. The image forming apparatus according to claim 12 or claim 14.

16. A circumferential member forming part of a conveyance path for conveying a recording medium, A holding member fixed to the circumferential member and rotating to hold the leading end portion of the recording medium, An image forming unit that forms an image on the recording medium at an image forming position in the circumferential path of the circumferential member, A sending unit that sends out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium, Having When the speed at which the holding member rotates by the circumferential member is the circumferential speed Vg, The conveyance speed of the recording medium is decelerated from a first conveyance speed V1 faster than the circumferential speed Vg before the holding position to a second conveyance speed V2 slower than the first conveyance speed V1. The time from when the recording medium starts to decelerate until it reaches the second conveyance speed V2 is constant. An image forming apparatus.

17. The time from when the recording medium starts to decelerate until it reaches the second conveyance speed V2 is set so that the deceleration is completed before the leading end portion of the recording medium enters the holding position. The image forming apparatus according to claim 16.

18. The deceleration to the second conveyance speed V2 is completed before the leading end portion of the recording medium enters the holding position. The image forming apparatus according to any one of claims 12 to 17.

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