Image forming apparatus

An image forming apparatus includes: a circulating member that is a part of a transport path that transports a recording medium; a holding member that is fixed to the circulating member, circulates, and holds a leading end portion of the recording medium; an image forming section that forms an image on the recording medium at an image forming position in a circulation path of the circulating member; and a feeding section that feeds out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium. When a circulation velocity Vg is defined as a velocity at which the circulating member circulates the holding member, a transport velocity of the recording medium is reduced from a first transport velocity V1, which is higher than the circulation velocity Vg, to a second transport velocity V2, which is lower than the first transport velocity V1, before the leading end portion of the recording medium enters the holding position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-137594 filed Aug. 25, 2021.

BACKGROUND

(i) Technical Field

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 59-007966 discloses a technology related to a transfer-sheet transport device of a recording apparatus. The transfer-sheet transport device moves, at a constant velocity, a recording head including a light-emitting-element array and an image forming system that are arranged substantially in the generatrix direction of a photoconductor drum that rotates at a constant velocity; forms a latent image by helically scanning the photoconductor drum; and transfers, to a transfer sheet, a toner image that is obtained by developing the latent image. In this technology, the transfer-sheet transport device includes: a pair of endless chains or belts that are transported in a direction at right angles to the axial line of the photoconductor drum; a gripper unit whose two ends are respectively fixed to the pair of endless chains or belts and that grips a leading end portion of the transfer sheet and transports the transfer sheet; and a unit that variably controls the positional relationship between the pair of chains or belts in the transport direction. The transfer-sheet transport device transports the transfer sheet in an inclined state by inclining the direction of the gripper unit at an angle that is the same as the angle between the scanning direction of helical recording on the photoconductor and the drum circumferential direction before transporting the transfer sheet to the transfer position.

SUMMARY

It is not possible or it is difficult for a holding member to hold a recording medium if the transport velocity of the recording medium when a feeding section feeds out the recording medium is the same as the circulation velocity of the holding member that is circulating and if the recording medium enters a holding position without changing the transport velocity.

Aspects of non-limiting embodiments of the present disclosure relate to suppression of failure of the circulating holding member in holding a recording medium, compared with a case where the recording medium fed out from the feeding section enters the holding position without changing a constant transport velocity.

According to an aspect of the present disclosure, there is provided an image forming apparatus including: a circulating member that is a part of a transport path that transports a recording medium; a holding member that is fixed to the circulating member, circulates, and holds a leading end portion of the recording medium; an image forming section that forms an image on the recording medium at an image forming position in a circulation path of the circulating member; and a feeding section that feeds out the recording medium to a holding position where the holding member holds the leading end portion of the recording medium, wherein when a circulation velocity Vg is defined as a velocity at which the circulating member circulates the holding member, a transport velocity of the recording medium is reduced from a first transport velocity V1, which is higher than the circulation velocity Vg, to a second transport velocity V2, which is lower than the first transport velocity V1, before the leading end portion of the recording medium enters the holding position.

DETAILED DESCRIPTION

Examples of an image forming apparatus according to exemplary embodiments of the present disclosure will be described.

First Exemplary Embodiment

Referring toFIGS.1to10, an image forming apparatus according to a first exemplary embodiment of the present disclosure will be described. An arrow UP shown in each figure indicates a vertically upward direction of the apparatus. As illustrated inFIG.1, an arrow RH indicates a horizontally rightward direction in the front view of the apparatus. In the following description, unless otherwise noted, “up-down direction” represents the up-down direction of the apparatus shown inFIG.1. In the following description, unless otherwise noted, “left-right direction” represents the leftward (=L) and rightward (=R) directions in the front view of the apparatus shown inFIG.1. In the following description, unless otherwise noted, “depth direction” (=front and back direction) represents the depth direction in the front view of the apparatus shown inFIG.1.

Overall Structure of Image Forming Apparatus

First, the configuration of an image forming apparatus10will be described.FIG.1is a front view schematically illustrating the image forming apparatus10according to the present exemplary embodiment.

As illustrated inFIG.1, the image forming apparatus10includes a unit10A disposed on the right side inFIG.1and a unit10B disposed on the left side inFIG.1. The unit10A, which is disposed on the right side inFIG.1, includes an image forming section11that forms an image on a sheet P, which is an example of a recording medium.

The image forming section11includes a liquid-droplet ejecting mechanism13for forming an image by using an inkjet method. The liquid-droplet ejecting mechanism13includes liquid-droplet ejection heads21Y,21M,21C, and21K that eject droplets of black (K), yellow (Y), magenta (M), and cyan (C), which are examples of color ink droplets, toward the sheep P, which is an example of a recording medium.

The liquid-droplet ejection head21Y, the liquid-droplet ejection head21M, the liquid-droplet ejection head21C, and the liquid-droplet ejection head21K are arranged in this order from upstream to downstream in the transport direction (described below) of the sheet P. The liquid-droplet ejection head21Y, the liquid-droplet ejection head21M, the liquid-droplet ejection head21C, and the liquid-droplet ejection head21K are arranged so that ejection surfaces23Y,23M,23C, and23K face a transfer member36described below (see alsoFIG.2). Color inks are supplied from ink tanks (not shown) to the liquid-droplet ejection heads21Y,21M,21C, and21K.

In the present exemplary embodiment, yellow (Y), magenta (M), cyan (C), and black (K) are basic colors for outputting a color image. In the following description, where it is not necessary to distinguish between the colors, “Y”, “M”, “C”, and “K” attached to the reference numerals will be omitted, and the term “liquid-droplet ejection head21” will be used.

The liquid-droplet ejection heads21Y,21M,21C, and21K for respective colors basically have the same structure, excluding the types of inks used. A method used by the liquid-droplet ejection head21to eject an ink droplet is not particularly limited. For example, a thermal method, a piezoelectric method, or the like may be used as a method of ejecting an ink droplet.

As illustrated inFIG.2, the liquid-droplet ejection heads21Y,21M,21C, and21K are each a full-line head that has a length corresponding to the width of an image recording region of the sheet P (seeFIG.1) and in which plural ink ejection nozzles (not shown) are arranged in the ejection surfaces23Y,23M,23C, and23K over the entire width of the image recording region. Each liquid-droplet ejection head21is immovably set to extend in a direction perpendicular to the transport direction of the sheet P (seeFIG.1).

In the present exemplary embodiment, an example in which an image is recorded by using four color inks of CMYK is described. However, the colors of inks and combinations of the colors are not limited to this example and may be changed. For example, as necessary, a light-color ink such as a light cyan ink or a light magenta ink, a thick-color ink, and a specific-color ink may be added. The order of arrangement of the heads for the colors is not limited to the order shown in the figures.

Transfer Member

As illustrated inFIGS.1,2, and7, the image forming apparatus10includes the transfer member36. The transfer member36has a cylindrical shape whose axial direction is the depth direction of the image forming apparatus10, and is rotatable in the circumferential direction. In an outer periphery of the transfer member36, a recess, in which a gripper42(described below) is to be accommodated, is formed. The transfer member36includes sprockets, around each of which a chain49(described below) is wrapped, at both end portions in the axial direction.

Image Forming Position

As illustrated inFIGS.1and2, an image forming position18(see alsoFIG.7) is a position where an image is formed by ejecting ink droplets to the sheet P from the ejection surface23(seeFIG.2) of each liquid-droplet ejection head21facing the transfer member36.

Sheet Transport Path

As illustrated inFIG.1, a sheet transport path A has a function of transporting the sheet P supplied from a sheet tray38. The image forming apparatus10according to the present exemplary embodiment includes plural sheet trays38. The sheet P, which is supplied from one of the sheet trays38, is transported along the sheet transport path A. Then, the sheet P passes through the image forming position18, and is output to a sheet output tray39.

To be more specific, the sheet transport path A extends through the unit10B, the unit10A, and the unit10B in order. Thus, the sheet P, which is transported along the sheet transport path A, is supplied from the sheet tray38disposed in the unit10B, passes through the unit10A, and is further returned to the unit10B.

On the other hand, the sheet transport path A branches off at a position downstream of a receiving position D2(described below) into a direction-changing path B for changing the transport direction of the sheet P. The direction-changing path B joins the sheet transport path A at a position further downstream in the transport direction. A part of the sheet transport path A between the direction-changing path B and a circulation path D is a joining path where a front-surface transport path of the sheet P and a back-surface transport path of the sheet P joins. The circulation path D will be described below. Each transport path includes plural sheet transport rollers (not shown). The sheet P is transported by the rollers along each transport path.

Image Forming Operation of forming Basic Image

Next, a basic image forming operation performed by the image forming apparatus10to form an image on the sheet P will be described.

Various actions in the image forming apparatus10are controlled by a controller16incorporated in the apparatus. When receiving an image forming command from the outside, the controller16activates the liquid-droplet ejecting mechanism13of the image forming section11. The controller16sends image data, which has been generated by an image signal processor (not shown) by image processing, to the image forming section11. Then, at the image forming position18, the liquid-droplet ejection head21for each color ejects ink droplets to the sheet P to form an image on the sheet P.

When duplex printing is performed, the sheet P passes through the receiving position D2(described below). Further, the transport direction of the sheet P is changed in the direction-changing path B provided in the transport path. Then, the sheet P is transported along a transport path C, which includes plural rollers (not shown), and is transported again to the sheet transport path A.

As illustrated inFIGS.3and4, the image forming apparatus10includes the gripper42that holds a leading end portion P1(seeFIG.3) of the sheet P, which is being transported, and that is an example of a holding member that assists in transportation of the sheet P. Plural clips44are arranged in the depth direction of the apparatus (seeFIG.3).

The gripper42includes the clips44, a rectangular case46that covers the clips44, and a shaft48that extends in the depth direction. The clips44are fixed to the shaft48, and are rotatable in accordance with rotation of the shaft48in the circumferential direction.

The case46extends in the depth direction, and is held by the shaft48. The case46rotates independently from rotation of the clips44. Moreover, the case46covers the clips44from the upstream side in the sheet transport direction, the downstream side in the sheet transport direction, and the back surface side of the sheet. The term “back surface” refers to a non-image-forming surface of the sheet P. With such a structure, tip portions45of the clips44and a fixed tab portion47at a back end of the case46can clamp a leading end portion P1of the sheet P in the transport direction. The reference numeral47A inFIGS.4A and4Brepresents a tip portion of the fixed tab portion47.

Chain

As illustrated inFIG.3, both end portions of the shaft48in the depth direction are held by the chains49for transport, each of which is an example of a circulating member. As the chains49circulate, the shaft48fixed to the chains49also circulates. Thus, the gripper42is held by the chains49, which are disposed in a front part and a back part of the image forming apparatus10, and circulates along a predetermined circulation path D (seeFIG.1).

As illustrated inFIG.7, the chains49are wrapped around the transfer member36, sprockets37that are disposed with a space therebetween in the depth direction, and the like, and are circulated by these members along the circulation path D.

Circulation Path D

As illustrated inFIG.1, a part of the circulation path D overlaps the sheet transport path A in a front view of the image forming apparatus10. To be specific, the circulation path D overlaps the sheet transport path A from a contact point with the sheet transport path A on the outer periphery of the sprocket37, which is disposed below the transfer member36, to the receiving position D2(described below).

At the start point of overlapping of the circulation path D with the sheet transport path A, the tip portions45of the clips44and the fixed tab portion47of the case46are close to each other, and the gripper42grips the leading end portion P1of the sheet P. A position in the circulation path D where the gripper42starts to hold the sheet P is a transfer position D1where the sheet P is transferred from the sheet transport path A to the gripper42.

At the end point of overlapping of the circulation path D with the sheet transport path A, the tip portions45of the clips44and the fixed tab portion47of the case46are separated from each other, and the leading end portion P1of the sheet P is released. A position in the circulation path D where the gripper42releases the sheet P is the receiving position D2where the sheet P is received by the sheet transport path A from the gripper42. The transfer position D1is located below the receiving position D2.

As illustrated inFIG.1, in the present exemplary embodiment, when the sheet is transferred from the transport path A to the circulation path D, the sheet P is transferred from the left side to the right side with respect to the image forming position. In other words, the sheet feed direction at the transfer position D1is a direction from the left side toward the right side.

On the other hand, when the sheet P is received by the circulation path D, the sheet P is received from the right side to the left side inFIG.1. In other words, the sheet discharge direction at the receiving position D2is from the right side to the left side.

A transport drum31is disposed at the receiving position D2in the circulation path D. Sprockets (described below), around which the chains49are wrapped, are provided at both end portions of the transport drum31in the axial direction.

Position Adjuster

As illustrated inFIG.1, a position adjuster50is disposed in the joining path in the sheet transport path A between the direction-changing path B and the transfer position D1.

As illustrated inFIG.5, the position adjuster50includes transport rollers51and52, registration rollers55and56, pass sensors62and64, and the like. Each roller is disposed above or below the sheet transport path A. The transport roller51on the upper side and the transport roller52on the lower side make a pair and rotate, the registration roller55on the lower side and the registration roller56on the lower side make a pair and rotate, and these pairs transport the sheet P.

Each of the pass sensors62and64detects whether or not the sheet P, which is being transported along the sheet transport path A, has passed. By using signals received from the pass sensors62and64, the controller16appropriately controls rotation of each of the transport rollers51and52and the registration rollers55and56.

Actions in Position Adjuster

As illustrated inFIG.5, when the leading end portion P1(seeFIG.3) of the sheet P reaches the registration rollers55and56, transportation of the sheet P temporarily stops, and the sheet P is fed out to the transfer position D1as the registration rollers55and56are rotated at a set timing. The timing at which the registration rollers55and56are rotated is controlled as the pass sensor62detects the timing of passage of the leading end portion P1of the sheet P.

Transfer of Sheet

As illustrated inFIGS.6A to6C, the sheet P that has passed through the position adjuster50is held by the fixed tab portion47of the case46and the tip portions45of the clips44of the gripper42on the circumference of the sprocket37inFIG.5. The gripper42is supplied while moving along the circulation path D in synchronism with the transport timing of the leading end portion P1of the sheet P.

At this time, as illustrated inFIG.6A, the case46and the clips44are in an opened state.

As illustrated inFIG.6B, while the gripper42moves along the circulation path D in synchronism with the transport timing of the sheet P, the case46and the clips44gradually become closer to each other. Then, the tip portions45of the clips44raise the leading end portion P1of the sheet P from the sheet transport path A.

As illustrated inFIG.6C, the leading end portion P1of the sheet P is further raised by the clips44and is transferred from the sheet transport path A to the circulation path D in a state in which the leading end portion P1is held between the fixed tab portion47of the case46and the tip portions45of the clips44. Subsequently, the sheet P is transported by the gripper42along the circulation path D.

A position where the sheet P is transferred from the sheet transport path A to the circulation path D is the transfer position D1.

Reversal of Sheet

As illustrated inFIG.1, after the sheet P has been transferred to the circulation path D, the sheet P is reversed along the outer periphery of the transfer member36. Then, the sheet P is transported to the image forming position18provided on the outer periphery of the transfer member36. That is, the second transfer position20is configured so that the sheet P passes through the second transfer position20in the process in which the sheet P is reversed along the circulation path and the outer periphery of the transfer member36.

A surface that faces a backup roller33when the sheet P passes through the image forming position18is an image forming surface and is the front surface. In other words, in the position adjuster50and at the transfer position D1, the sheet P is transported in a state in which the back surface of the sheet P, which is a non-image-forming surface, faces upward.

Reception of Sheet

The sheet P is received by the sheet transport path A from the circulation path D. The branching point between the circulation path D and the sheet transport path A is the receiving position D2. At the receiving position D2, the sheet P is received by the sheet transport path A from the circulation path D as the gripper42, which is holding the leading end portion P1(seeFIG.3) of the sheet P, is opened.

Partial Configurations

Next, partial configurations of the present exemplary embodiment will be described.

The controller16illustrated inFIG.11has a function of controlling the entirety of the image forming apparatus10. The hardware configuration of the controller16is a computer including: a central processing unit (CPU) (not shown), a read only memory (ROM) storing programs and the like for realizing each process routine, a random access memory (RAM) for temporarily storing data, a memory as a storage unit a network interface, and the like.

A chain driving mechanism79illustrated inFIG.11circulates the transfer member36and the sprockets37(seeFIG.5and other figures), around which the chains49are wrapped, and the like. The circulation velocity and the like of the chain driving mechanism79are controlled by the controller16.

As illustrated inFIG.5, the pass sensor64for detecting the leading end portion P1(seeFIG.3) of the sheet P is disposed at a pass position TS (seeFIG.9) between the registration rollers55and56and the transfer position D1in the sheet transport path A. A pass signal KS is defined as a signal indicating that the pass sensor64has detected the leading end portion P1(seeFIG.3) of the sheet P at the pass position TS.

The image forming apparatus10includes a period sensor202for detecting the period of rotation of the sprocket37. The period sensor202detects a detection portion204of the sprocket37every time the sprocket37rotates once. A period signal SS is defined as a signal detected by the period sensor202when the period sensor202detects the detection portion204every time the sprocket37rotates once.

As illustrated inFIG.11, the pass signal KS detected by the pass sensor64and the period signal SS detected by the period sensor202are sent to the controller16(see alsoFIG.1).

As illustrated inFIG.10, the chain49has a structure such that roller links59, which are formed by assembling link plates and bushes onto which freely rotatable rollers are fitted, are connected to each other via pin links57.

Plural grippers42are fixed to the chain49at predetermined intervals. The number L1of links between the grippers42that are adjacent to each other and fixed to the chain49coincides with the number L2of teeth, which is the total number of teeth129of the sprocket37. Thus, an entry period GS, which is a period at which the grippers42enter the transfer position D1, coincides with a rotation period PS, which is a period at which the sprocket37rotates once. Note that the number L1of links between the grippers42that are adjacent to each other includes the number of roller links59to which the grippers42are fixed.

The position adjuster50illustrated inFIG.5can adjust the transport velocity of the sheet P, which has been fed out, by adjusting the rotation velocity of the registration rollers55and56and the like. The transport velocity of the sheet P, which is controlled by the position adjuster50, is controlled by the controller16(seeFIG.11). The transport velocity of the sheet P is controlled so that the leading end portion P1(seeFIG.3) of the sheet P enters the transfer position D1after the transport velocity has decreased from that when the position adjuster50feeds out the sheet P.

To be specific, the controller16(seeFIG.11) performs control so that the following relationships hold:
V1>Vg,
V1>V2, and
V2≈Vg,

where Vg (m/s) is the circulation velocity of the gripper42,

V1(m/s) is a first transport velocity that is the transport velocity of the sheet P when the position adjuster50feeds out the sheet P, and

V2(m/s) is a second transport velocity that is the transport velocity of the sheet P when the leading end portion P1(seeFIG.3) of the sheet P is at the transfer position D1.

V1is in the range of greater than or equal to 1.02 times Vg to less than or equal to 1.09 times Vg. In the present exemplary embodiment, V1=Vg×1.05. V2is in the range of Vg±1%, and, in the present exemplary embodiment, V2=Vg×1.005. These ranges are examples, and are not limited to these. These ranges may be appropriately set in accordance with specifications such as the circulation velocity. It is sufficient that at least “V1>Vg” and “V1>V2” are satisfied.

The circulation velocity Vg (m/s) of the gripper42is the same as the rotation velocity of the sprockets37.

Moreover, in the present exemplary embodiment, the controller16(seeFIG.11) controls a timing TA (seeFIG.9), at which the sheet P starts to decelerate to the second transport velocity V2, so that the leading end portion P1of the sheet P (seeFIGS.6A to6CandFIGS.8A to8F) enters the transfer position D1when the gripper42moves to the transfer position D1. A timing TB (seeFIG.9) is defined as a timing at which the sheet P finishes decelerating to the second transport velocity V2.

A time interval TC between the timing TA and the timing TB illustrated inFIG.9is controlled to be constant. The timing TB, at which the sheet P finishes decelerating to the second transport velocity V2, is set so that the timing TB is earlier than the time when the leading end portion P1of the sheet P (seeFIGS.6A to6CandFIGS.8A to8F) enters the transfer position D1.

To be specific, as illustrated inFIG.8A, the position adjuster50feeds out the sheet P at the first transport velocity V1. As illustrated inFIG.8B, the controller16controls the position adjuster50to start to decelerate the sheet P to the second transport velocity V2. As illustrated inFIG.8C, in a state in which the sheet P has decelerated to the second transport velocity V2, the leading end portion P1of the sheet P enters the transfer position D1. The transfer position D1in the present exemplary embodiment is a position that is forward from the tip portion47A of the fixed tab portion47by W (mm) in the transport direction. In the present exemplary embodiment, W is 5 mm.

From a different viewpoint, the position adjuster50feeds out the sheet P at a transport velocity higher than the circulation velocity of the gripper42, and the transport velocity of the sheet P is reduced after the leading end portion P1of the sheet P has entered into the gripper42. The phrase “enter into the gripper42” represents that the sheet P enters a space between the case46and the clips44of the gripper42. To be more specific, this is a state in which an imaginary line connecting the tip of the case46and the tips of the clips44intersects the sheet P.

Then, as illustrated inFIGS.8D to8F, the gripper42holds the leading end portion P1of the sheet P and transports the sheet P.

In the present exemplary embodiment, the controller16(seeFIG.11) adjusts the timing TA (seeFIG.8B), at which the sheet P starts to decelerate to the second transport velocity V2, by using the time difference t between the period signal SS of the sprocket37, which is detected by the period sensor202(seeFIG.5), and the pass signal KS, which indicates that the pass sensor64has detected the leading end portion P1(seeFIG.3) of the sheet P at the pass position TS (seeFIG.5).

To be specific, the controller16(seeFIG.1) performs control as follows.

A reference value t0is defined as a reference value of a designed time difference t, and a reference timing TD is defined as a reference value of a timing at which the sheet P is designed to start to decelerate. An actually measured value t1is defined as the time difference between the period signal SS and the pass signal KS that are actually detected by the pass sensor64and the period sensor202, and Δt is defined as the time difference between the actually measured value t1and the reference value t0. The controller16(seeFIG.11) sets the timing TA based on the reference timing TD and Δt.

From a different viewpoint, if the actually measured value t1of the time difference between the pass signal KS and the period signal SS is large, the timing TA, at which the sheet P starts to decelerate to the second transport velocity V2, is advanced compared with a case where t1is small.

Operational Effects

Next, operational effects of the present exemplary embodiment will be described.

The controller16performs control so that the following relationships hold:
V1>Vg, and
V1>V2,

where Vg (m/s) is the circulation velocity of the gripper42,

V1(m/s) is the first transport velocity that is the transport velocity of the sheet P when the position adjuster50feeds out the sheet P, and

V2(m/s) is the second transport velocity that is the transport velocity of the sheet P when the leading end portion P1of the sheet P is at the transfer position D1.

From a different viewpoint, the controller16performs control so that the position adjuster50feeds out the sheet P at a transport velocity higher than the circulation velocity of the gripper42and so that the transport velocity of the sheet P is reduced after the leading end portion P1of the sheet P has entered into the gripper42.

Thus, it is possible to suppress failure of the gripper42in holding the leading end portion P1of the sheet P, compared with a case where the leading end portion P1of the sheet P fed out by the position adjuster50enters the transfer position D1without changing a constant transport velocity.

Here, the above fact will be described in detail.

As a first comparative example, a case where the leading end portion P1of the sheet P enters the transfer position D1without changing the first transport velocity V1, at which the position adjuster50has fed out the sheet P, is assumed. In this case, because the transport velocity of the sheet P at the transfer position D1is higher the circulation velocity Vg of the gripper42, failure of the gripper42in holding the leading end portion P1of the sheet P tends to occur.

As a second comparative example, a case where the position adjuster50feeds out the sheet P at the second transport velocity V2and the leading end portion P1enters the transfer position D1without changing the transport velocity is assumed. In this case, the transport velocity of the sheet P when the position adjuster50feeds out the sheet P is the substantially same as the circulation velocity of the gripper42. Thus, the leading end portion P1of the sheet P cannot catch up the gripper42and it is not possible or is difficult for the gripper42to hold the leading end portion P1, and holding failure tends to occur.

In contrast, with the present exemplary embodiment, the gripper42can easily hold the leading end portion P1of the sheet P and occurrence of holding failure is suppressed, by making the first transport velocity V1, at which the position adjuster50feeds out the sheet P, be higher than the circulation velocity Vg of the gripper42and by making the second transport velocity V2, which is the transport velocity of the sheet P when the leading end portion P1of the sheet P is at the transfer position D1after decelerating thereafter, be the same as or substantially the same as the circulation velocity Vg.

In the present exemplary embodiment, the timing at which the sheet P starts to decelerate to the second transport velocity V2is adjusted so that the leading end portion P1of the sheet P enters the transfer position D1when the gripper42moves to the transfer position D1.

Thus, the controller16can easily perform control, compared with a case where the leading end portion P1of the sheet P is made to enter the transfer position D1when the gripper42moves to the transfer position D1by adjusting the length of time during which the transport velocity of the sheet P decreases from the first transport velocity V1to the second transport velocity V2, that is, the length of the time interval TC between the timing TA and the timing TB.

In the present exemplary embodiment, the rotation period PS, which is a period at which the sprocket37rotates once, coincides with the entry period GS, which is a period at which the grippers42enter the transfer position D1. Thus, it is possible to estimate the timing at which each gripper42enters the transfer position D1with high accuracy by using the period signal SS of the sprocket37detected by the period sensor202.

The timing TA, at which the sheet P starts to decelerate to the second transport velocity V2, is adjusted by using the period signal SS of the sprocket37detected by the period sensor202and the pass signal KS, which indicates that the pass sensor64has detected the leading end portion P1of the sheet P at the pass position TS. Thus, it is possible to adjust the timing TA, at which the sheet P starts to decelerate to the second transport velocity V2, with high accuracy compared with, for example, a case where only the pass signal KS is used.

With the present exemplary embodiment, by making the number L1of links between the grippers42that are adjacent to each other and that are fixed to the chain49be the same as the number L2of teeth, which is the total number of the teeth129of the sprocket37, it is possible to make the rotation period PS, at which the sprocket37rotates once, coincide with the entry period GS, at which the grippers42enter the transfer position D1.

In the present exemplary embodiment, the period during which the transport velocity of the sheet P decreases from the first transport velocity V1to the second transport velocity V2, that is, the time interval TC between the timing TA and the timing TB is constant. Thus, the timing at which the leading end portion P1of the sheet P enters the transfer position D1is stable, compared with a case where the time interval TC is not constant.

In the present exemplary embodiment, the sheet P has finished decelerating to the second transport velocity V2before the leading end portion P1of the sheet P enters the transfer position D1. Thus, the gripper42can stably hold the leading end portion P1of the sheet P, compared with a case where the sheet P finishes decelerating to the second transport velocity V2after the leading end portion P1of the sheet P has entered the transfer position D1.

Second Exemplary Embodiment

An image forming apparatus according to a second exemplary embodiment of the present disclosure will be described. Partial configurations will only be described, because the image forming apparatus according to the second exemplary embodiment differs from the first exemplary embodiment only in partial configurations. Redundant description will be omitted or simplified, and the same members and the like will be denoted by the same reference numerals.

Partial Configurations

Next, the partial configurations of the present exemplary embodiment will be described.

The controller16(seeFIG.11) performs control so that the following relationships hold:
V1>Vc>Vg,
V1>Vc>V2, and
V2≈Vg

where Vg (m/s) is the circulation velocity of the gripper42,

V1(m/s) is the first transport velocity that is the transport velocity of the sheet P when the position adjuster50feeds out the sheet P,

V2(m/s) is the second transport velocity that is the transport velocity of the sheet P when the leading end portion P1(seeFIG.3) of the sheet P is at the transfer position D1, and

Vc (m/s) is an intermediate transport velocity between the first transport velocity V1(m/s) and the second transport velocity V2(m/s).

V1is in the range of greater than or equal to 1.02 times Vg to less than or equal to 1.09 times Vg. In the present exemplary embodiment, V1=Vg×1.05. V2is in the range of Vg±1%, and, in the present exemplary embodiment, V2=Vg×1.005. In the present exemplary embodiment, Vc=(V1+V2)/2. These ranges are examples, and are not limited to these. These ranges may be appropriately set in accordance with specifications such as the circulation velocity. It is sufficient that at least “V1>Vc>Vg” and “V1>Vc>V2” are satisfied.

The circulation velocity Vg (m/s) of the gripper42is the same as the rotation velocity of the sprockets37.

As illustrated inFIG.14, the controller16(seeFIG.11) performs control so that, after reducing the transport velocity of the sheet P when the position adjuster50feeds out the sheet P from the first transport velocity V1to the intermediate transport velocity Vc and transporting the sheet P, the position adjuster50decelerates the sheet P to the second transport velocity V2and the leading end portion P1(seeFIG.3) of the sheet P enters the transfer position D1.

The sheet P starts to decelerate from the intermediate transport velocity Vc to the second transport velocity V2at a predetermined timing TQ. The timing TQ is before the transfer position D1by CW, and CW is 10 mm in the present exemplary embodiment.

In the present exemplary embodiment, the controller16(seeFIG.11) controls a timing TP, at which the sheet P starts to decelerate to the intermediate transport velocity Vc, so that the leading end portion P1of the sheet P (seeFIGS.6A to6CandFIGS.8A to8F) enters the transfer position D1.

The timing TR, at which the sheet P finishes decelerating from the intermediate transport velocity Vc to the second transport velocity V2, is set so that the timing TR is earlier than the time when the leading end portion P1of the sheet P (seeFIGS.6A to6CandFIGS.8A to8F) enters the transfer position D1.

To be specific, as illustrated inFIG.13A, the position adjuster50feeds out the sheet P at the first transport velocity V1. As illustrated inFIG.13B, the controller16controls the position adjuster50to reduce the transport velocity of the sheet P to the intermediate transport velocity Vc and to transport the sheet P at the intermediate transport velocity Vc. As illustrated inFIG.13C, the controller16controls the position adjuster50to decelerate the sheet P from the intermediate transport velocity Vc to the second transport velocity V2at the predetermined timing TR (seeFIG.14) and to make the leading end portion P1of the sheet P enter the transfer position D1in a state in which the sheet P has finished decelerating to the second transport velocity V2. The transfer position D1in the present exemplary embodiment is a position that is forward from the tip portion47A of the fixed tab portion47by W (mm) in the transport direction. In the present exemplary embodiment, W is 5 mm. Then, as illustrated inFIGS.13D to13F, the gripper42holds the leading end portion P1of the sheet P and transports the sheet P.

In the present exemplary embodiment, the controller16(seeFIG.11) adjusts the timing TP (seeFIG.14), at which the sheet P starts to decelerate to the intermediate transport velocity Vc, by using the time difference t between the period signal SS of the sprocket37, which is detected by the period sensor202(seeFIG.5), and the pass signal KS, which indicates that the pass sensor64has detected the leading end portion P1(seeFIG.3) of the sheet P at the pass position TS (seeFIG.5).

To be specific, the controller16(seeFIG.1) performs control as follows.

A reference value t0is defined as a reference value of a designed time difference t, and a reference timing TD is defined as a reference value of a timing at which the sheet P is designed to start to decelerate. An actually measured value t1is defined as the time difference between the period signal SS and the pass signal KS that are actually detected by the pass sensor64and the period sensor202, and Δt is defined as the time difference between the actually measured value t1and the reference value t0. The controller16(seeFIG.11) sets the timing TP (seeFIG.14) based on the reference timing TD and Δt.

From a different viewpoint, if the actually measured value t2of the time difference between the pass signal KS and the period signal SS is large, the timing TP, at which the sheet P starts to decelerate to the intermediate transport velocity Vc, is advanced compared with a case where t1is small.

Operational Effects

Next, operational effects of the present exemplary embodiment will be described.

The controller16performs control so that the following relationships hold:
V1>Vc>Vg, and
V1>Vc>V2

where Vg (m/s) is the circulation velocity of the gripper42,

V1(m/s) is the first transport velocity that is the transport velocity of the sheet P when the position adjuster50feeds out the sheet P,

V2(m/s) is the second transport velocity that is the transport velocity of the sheet P when the leading end portion P1(seeFIG.3) of the sheet P is at the transfer position D1, and

Vc (m/s) is the intermediate transport velocity between the first transport velocity V1(m/s) and the second transport velocity V2(m/s).

The controller16performs control so that, after reducing the transport velocity of the sheet P when the position adjuster50feeds out the sheet P from the first transport velocity V1to the intermediate transport velocity Vc and transporting the sheet P, the position adjuster50decelerates the sheet P to the second transport velocity V2and the leading end portion P1of the sheet P enters the transfer position D1.

Thus, it is possible to suppress failure of the gripper42in holding the leading end portion P1of the sheet P, compared with a case where the leading end portion P1of the sheet P fed out by the position adjuster50enters the transfer position D1without changing a constant transport velocity.

Moreover, the accuracy with which the leading end portion P1of the sheet P enters the transfer position D1in a state in which the transport velocity is reduced to the second transport velocity V2is improved, compared with a case where the transport velocity is reduced directly from the first transport velocity V1to the second transport velocity V2. Therefore, it is possible to further suppress failure of the gripper42in holding the leading end portion P1of the sheet P.

In the present exemplary embodiment, the timing at which the sheet P starts to decelerate to the intermediate transport velocity Vc is adjusted so that the leading end portion P1of the sheet P enters the transfer position D1when the gripper42moves to the transfer position D1. Thus, the controller16can easily perform control compared with a case where the leading end portion P1of the sheet P is made to enter the transfer position D1when the gripper42moves to the transfer position D1by adjusting the length of time during which the transport velocity of the sheet P decreases from the first transport velocity V1to the intermediate transport velocity Vc.

In the present exemplary embodiment, the rotation period PS, which is a period at which the sprocket37rotates once, coincides with the entry period GS, which is a period at which the grippers42enter the transfer position D1. Thus, it is possible to estimate the timing at which each gripper42enters the transfer position D1with high accuracy by using the period signal SS of the sprocket37detected by the period sensor202.

The timing TQ, at which the sheet P starts to decelerate to the intermediate transport velocity Vc, is adjusted by using the period signal SS of the sprocket37detected by the period sensor202and the pass signal KS, which indicates that the pass sensor64has detected the leading end portion P1of the sheet P at the pass position TS. Thus, it is possible to adjust the timing TQ, at which the sheet P starts to decelerate to the intermediate transport velocity Vc, with high accuracy compared with, for example, a case where only the pass signal KS is used.

With the present exemplary embodiment, by making the number L1of links between the grippers42that are adjacent to each other and that are fixed to the chain49be the same as the number L2of teeth, which is the total number of the teeth129of the sprocket37, it is possible to make the rotation period PS, at which the sprocket37rotates once, coincide with the entry period GS, at which the grippers42enter the transfer position D1.

In the present exemplary embodiment, the sheet P has finished decelerating to the second transport velocity V2before the leading end portion P1of the sheet P enters the transfer position D1. Thus, the gripper42can stably hold the leading end portion P1of the sheet P, compared with a case where the sheet P finishes decelerating to the second transport velocity V2after the leading end portion P1of the sheet P has entered the transfer position D1.

Modification

Next, a modification of the second exemplary embodiment will be described.

In the exemplary embodiments described above, the timing TQ at which the sheet P starts to decelerate from the intermediate transport velocity Vc to the second transport velocity V2, which is illustrated inFIG.14, is constant. However, the controller16(seeFIG.11) in the modification adjusts the timing TQ in accordance with the type of the sheet P.

To be specific, if the stiffness of the sheet P is low, the leading end portion P1of the sheet P may become curved and the leading end portion P1may enter the transfer position D1with a time lag, and therefore it is necessary to delay the timing TQ to compensate for the time lag.

Thus, in the present modification, the timing TQ is adjusted in accordance with the type of the sheet P. That is, if the stiffness of the sheet P is low due to a small thickness or the like, the timing TQ is delayed compared with a case where the stiffness of the sheet P is high due to a large thickness or the like.

To be specific, the controller16stores timing TQ corresponding to each type of the sheet P, and starts to decelerate the sheet P to the intermediate transport velocity Vc at the stored timing TQ. The type of the sheet P may be detected by a sensor, or a user may input the type of the sheet P from an operation panel or the like.

In this way, the controller16(seeFIG.11) adjusts the timing TQ in accordance with the type of the sheet P. Therefore, it is possible to further suppress failure of the gripper42in holding the leading end portion P1of the sheet P, compared with a case where the timing TQ is constant.

The term “stiffness” of the sheet P refers to resistance generated when a bending force is applied to the sheet P. From a different viewpoint, the stiffness of the sheet P is the rigidity of the sheet P.

Another Example of Image Forming Section

Next, another example of the image forming section of the image forming apparatus according to the first exemplary embodiment and the second exemplary embodiment will be described.

An image forming section99illustrated inFIG.12includes an image forming unit12(described below) for forming an image by using an electrophotographic method, an intermediate transfer belt22for holding the formed image, and an intermediate transfer unit14for mounting and supporting the intermediate transfer belt22. In the image forming apparatus10, a transfer member36for transferring an image from the intermediate transfer unit14to the sheet P for image recording is disposed on the left lower side of the intermediate transfer unit14.

A second transfer position20is an example of an image forming position where the intermediate transfer belt22and the transfer member36are in contact with each other. At the second transfer position20, a toner image that is formed by the image forming unit12is transferred to a surface of the sheet P via the intermediate transfer belt22mounted in the intermediate transfer unit14.

The image forming section99includes plural image forming units12for respectively forming toner layers of different colors. In the present exemplary embodiment, the image forming section99includes four image forming units12, which are a yellow image forming unit12Y, a magenta image forming unit12M, a cyan image forming unit12C, and a black image forming unit12K, corresponding to respective colors.

Yellow (Y), magenta (M), cyan (C), and black (K) are four colors for outputting a color image. In the following description, unless it is necessary to distinguish between the colors, each the image forming unit12will be simply referred to as “image forming unit12”, without using a character Y, M, C, or K.

The image forming units12for the respective colors basically have the same configuration, except for the types of toners used. Each image forming unit12includes a cylindrical photoconductor24that rotates and a charger26that charges the photoconductor24. The image forming unit12includes an exposure device28, which forms an electrostatic latent image by irradiating the charged photoconductor24with exposure light, and a developing device30, which develops electrostatic latent image into an image formed of toner layers by using a developer. The image forming unit12further includes a cleaner29that removes toner that remains on the surface of the photoconductor24after toner has been transferred from the photoconductor24to the intermediate transfer belt22.

The photoconductor24for each color is capable of being in contact with the outer peripheral surface of the intermediate transfer belt22. The image forming units12corresponding to yellow, magenta, cyan, and black are arranged from the upstream side toward the downstream side in the circulation direction of the intermediate transfer belt22.

Intermediate Transfer Unit

The intermediate transfer unit14includes first transfer rollers34facing the image forming units12for the respective colors and a backup roller33facing the transfer member36.

Intermediate Transfer Belt

The intermediate transfer belt22is an endless belt. The intermediate transfer belt22is wrapped around plural rollers32to assume a position as follows. In the present exemplary embodiment, in a front view, the position of the intermediate transfer belt22has a substantially obtuse-triangular shape that is long in the apparatus width direction and that has an obtuse-angle vertex in the downward direction. One of the plural rollers32(not shown) has a function of receiving motive power of a motor and rotating the intermediate transfer belt22in the direction of arrow X. The intermediate transfer belt22transports a first-transferred image to the second transfer position20by rotating in the direction of arrow X.

The intermediate transfer belt22can circulate in the direction of arrow X in a state of being in contact with or separated from the photoconductors24for the respective colors.

First Transfer

Each first transfer region19is composed of a contact portion where the photoconductor24, the intermediate transfer belt22, and the first transfer roller34are in contact with each other. The first transfer roller34faces the photoconductor24with the intermediate transfer belt22therebetween. The first transfer roller34and the intermediate transfer belt22are in contact with each other with a predetermined load.

To the first transfer roller34, a predetermined voltage is applied by a power supply (not shown). The voltage is a first transfer voltage for first transferring a toner image, which has been formed on the photoconductor24, to the intermediate transfer belt22at a position between the photoconductor24and the first transfer roller34.

Transfer Member

The transfer member36is disposed at a position facing the backup roller33with the intermediate transfer belt22therebetween. The transfer member36has a cylindrical shape whose axial direction is the depth direction of the image forming apparatus10, and is rotatable in the circumferential direction.

To the transfer member36, a voltage is applied by a power supply (not shown). The voltage is a second transfer voltage for second transferring toner images, which have been overlappingly transferred to the intermediate transfer belt22, to the sheet P transported to the second transfer position20.

Second Transfer

The second transfer position20is formed of a contact portion where the intermediate transfer belt22and the transfer member36, having a roller-like shape, are in contact with each other. The intermediate transfer belt22and the transfer member36are in contact with each other with a predetermined load due to the backup roller33facing the transfer member36.

Fixing Device

A fixing device40is disposed downstream of the second transfer position20in the transport direction of the sheet P. The fixing device40includes a transport drum31and a heating roller43that face each other. The transport drum31and the heating roller43face each other with the sheet transport path A (described above) therebetween. That is, the sheet P, to which an image is to be fixed, is transported so as to pass between the transport drum31and the heating roller43.

Image Forming Operation of forming Basic Image

Next, an overview of a basic image forming operation performed by the image forming section99on the sheet P will be described.

When receiving an image forming command from the outside, the controller16activates each image forming unit12. The photoconductor24for each color is charged by the charger26while rotating. The controller16sends image data, which has been image-processed by an image signal processor (not shown), to each exposure device28. Each exposure device28irradiates a corresponding photoconductor24with light, and thereby exposes the charged photoconductor24with the light. Thus, an electrostatic latent image is formed on the outer peripheral surface of each photoconductor24. The electrostatic latent image formed on each photoconductor24is developed by a corresponding developing device30, and a toner image for each color is formed on the photoconductor24.

Each color toner image formed on the photoconductor24for the color is first-transferred to the intermediate transfer belt22by the first transfer roller34for the color in each first transfer region. At this time, as the intermediate transfer belt22circulates, the color toner images are successively first-transferred to the intermediate transfer belt22while being superposed on each other. The toner images that have been superposed in this way are transported to the second transfer position20as the intermediate transfer belt22circulates. Then, the superposed toner images are transferred from the intermediate transfer belt22to the sheet P at the second transfer position20.

The sheet P, onto which the toner images have been second-transferred, is transported toward the fixing device40. In the fixing device40, the fixing roller heats and presses the sheet P. Thus, the toner images, which have been formed by the image forming units12, are fixed to the sheet P.

In duplex printing, the transport direction of the sheet P that has passed through the fixing device40is changed in the direction-changing path B of the transport path. Then, the sheet P is transported along the transport path C, which includes plural rollers (not shown), again to the sheet transport path A.

Others

The present disclosure is not limited to the exemplary embodiments described above.

For example, in the exemplary embodiments described above, the transport velocity when the position adjuster50feeds out the sheet P is the first transport velocity V1(m/s). However, the transport velocity is not limited to this. The position adjuster50may feed out the sheet P at a third transport velocity V3that is higher or lower than the first transport velocity V1(m/s), and subsequently, may change the transport velocity from the third transport velocity V3to the first transport velocity V1(m/s).

If the third transport velocity V3is lower than the first transport velocity V1(m/s), the magnitude relationship between the third transport velocity V3and the circulation velocity Vg of the gripper42(m/s) is not specified. That is, any of V3>Vg, V3=Vg, and V3<Vg may hold.

If the third transport velocity V3is lower than the first transport velocity V1(m/s), the magnitude relationship between the third transport velocity V3and the second transport velocity V2is not specified. That is, any of V3>V2, V3=V2, and V3<V2may hold.

For example, in the exemplary embodiments described above, the timing TA, at which the sheet P starts to decelerate to the second transport velocity V2, or the timing TQ, at which the sheet P starts to decelerate to the intermediate transport velocity Vc, is adjusted by using the period signal SS of the sprocket37, which is detected by the period sensor202, and the pass signal KS, which indicates that pass sensor64has detected the leading end portion P1of the sheet P at the pass position TS. However, a method of adjusting the timings is not limited to this. The timing TA at which the sheet P starts to decelerate to the second transport velocity V2or the timing TQ at which the sheet P starts to decelerate to the intermediate transport velocity Vc may be adjusted by using another signal.

For example, in the exemplary embodiments described above, the timing at which the sheet P starts to decelerate to the second transport velocity V2or the timing TQ at which the sheet P starts to decelerate to the intermediate transport velocity Vc is adjusted so that the leading end portion P1of the sheet P enters the transfer position D1when the gripper42moves to the transfer position D1. However, the timing is not limited to this. The timing TA at which the sheet P starts to decelerate to the second transport velocity V2or the timing TQ at which the sheet starts to decelerate to the intermediate transport velocity Vc may be fixed.

For example, the image forming section99of the exemplary embodiment described above, which uses an electrophotographic method, transfers a toner image held by the intermediate transfer belt22, which is an example of an image carrier and an intermediate transfer member, to the sheet P. However, the configuration of the image forming apparatus is not limited to this. The image forming apparatus may transfer a toner image held by a photoconductor, which is an example of an image carrier, to a recording medium.

For example, in the exemplary embodiments described above, the image forming method used in the image forming section is an inkjet method or an electrophotographic method. However, the image forming method is not limited to these. The image forming section may use another image forming method, such as an offset printing method.

For example, in the exemplary embodiments described above, the gripper42, which is an example of a holding member, is used as a member for physically holding the leading end portion P1of the sheet P. However, the structure of a holding member is not limited to such a structure, and may be a structure for holding the leading end portion of the sheet P by using an air suction force.

For example, the circulating member, which is a chain in the exemplary embodiments described above, is not limited to a chain. For example, the circulating member may be a belt.

The configuration of the image forming apparatus is not limited to those of the exemplary embodiments described above, and may be any appropriate configuration. Moreover, the present disclosure may be carried out in any appropriate mode within the spirit and scope of the present disclosure.