JP5174756B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, or a complex machine of these.

  2. Description of the Related Art Conventionally, as an apparatus for forming (printing) an image on a sheet as a transfer material, an image forming apparatus such as a copier, a printer, a facsimile, or a complex machine of these is known. In the image forming apparatus, a charging step for charging the surface of the photosensitive drum, an exposure step for irradiating the charged photosensitive drum with laser light to form an electrostatic latent image on the surface of the photosensitive drum, and the surface of the photosensitive drum A developing process for developing the toner by attaching toner to the electrostatic latent image formed thereon, a transferring process for transferring the toner image formed from the toner attached to the surface of the photosensitive drum to the paper, and the toner transferred to the paper An image is formed on the paper by sequentially performing each of the fixing steps for fixing the image on the paper.

  Of the above processes, the transfer process is performed on the sheet conveyed to the transfer nip. Therefore, it is necessary to transport the paper to the transfer nip prior to the transfer process. In the case of the so-called direct transfer system, the transfer nip is formed, for example, between the photosensitive drum and the transfer roller. In the case of the so-called indirect transfer method, the transfer nip is formed, for example, between the intermediate transfer belt and the transfer roller.

  On the upstream side of the transfer nip, a sheet detection sensor for detecting a sheet, a registration roller pair, and the like are disposed. The registration roller pair is provided for the purpose of correcting the skew of the paper (oblique feeding), matching the timing of the paper with the formation of the toner image in the image forming unit, and the like. The registration roller pair carries out the correction and timing adjustment based on the detection signal information from the paper detection sensor, and conveys the paper toward the transfer nip.

  In the image forming apparatus, a pair of paper feed rollers as an upstream roller pair and an intermediate roller pair as a downstream roller pair are disposed between the registration roller pair and a paper feed cassette for storing paper. Have been. The pair of paper feed rollers includes a paper feed drive roller and a separation roller including a driven roller. The intermediate roller pair is disposed on the downstream side of the paper feed roller pair and includes an intermediate drive roller and an intermediate driven roller.

  The separation roller is provided to separate the sheets fed by the paper feed driving roller one by one. That is, the separation roller is provided in order to prevent double feeding of sheets (feeding out a plurality of sheets in a stacked state). The separation roller is generally formed of a material having a high friction coefficient such as rubber on the surface (circumferential surface). According to the separation roller, by using this high coefficient of friction, when the paper comes into contact with the paper from the opposite side of the paper feed driving roller and the paper is likely to be double-fed, the paper that comes into contact with the separation roller Can be prevented from being sent out (see, for example, Patent Documents 1 and 2 below).

The paper stored in the paper feed cassette is sequentially sent out by the paper feed roller pair and the intermediate roller pair, and is conveyed toward the registration roller pair (the paper feed to this registration roller pair is also referred to as “primary paper feed”). ). After the paper reaches the registration roller pair, skew correction is performed by the registration roller pair, and then the paper is conveyed toward the transfer nip (feeding from the registration roller pair to the transfer nip is “secondary feeding”). Paper ").
In the conventional image forming apparatus, when the primary paper feeding is finished, the rotation driving of the paper feeding driving roller in the paper feeding roller pair and the rotational driving of the intermediate driving roller in the intermediate roller pair are controlled to be stopped simultaneously. ing.

JP-A-7-206197 JP-A-9-77294

  However, even if it is attempted to stop the rotation driving of the sheet feeding driving roller and the rotation driving of the intermediate driving roller simultaneously when the primary sheet feeding is finished, the rotation of the sheet feeding driving roller and the intermediate driving roller are actually stopped. In many cases, the rotation of the motor does not stop at the same time. For example, a configuration in which the paper feed drive roller and the intermediate drive roller are rotationally driven by a drive source via a clutch is common, but in such a configuration, paper feed drive is performed due to variations in the intermittent timing of the clutch. It is difficult to stop the rotation of the roller and the rotation of the intermediate driving roller at the same time.

  Here, when the paper feed drive roller located on the upstream side stops later than the intermediate drive roller located on the downstream side, the sheet is bent between the paper feed roller pair and the intermediate roller pair, This reduces the load applied to the surface of the separation roller. As a result, the slippage of the sheet tends to occur on the surface of the separation roller, and uneven wear tends to occur on the surface of the separation roller. As a result, the effect of preventing the double feeding of sheets by the separation roller is reduced.

  Accordingly, the present invention provides an upstream roller pair having a driving roller and a driven roller, a downstream roller pair disposed downstream of the upstream roller pair, and a registration roller pair disposed downstream of the downstream roller pair. And an image forming apparatus capable of suppressing slippage of a transfer material on the surface of the driven roller and suppressing uneven wear on the surface of the driven roller.

  The present invention includes an upstream roller having a first driving roller and a first driven roller, and sandwiching and transporting a sheet-shaped transfer material between the first driving roller and the first driven roller. A pair of rollers and a second drive roller and a third roller disposed between the pair of upstream rollers and the pair of upstream rollers between the second drive roller and the third roller. A downstream roller pair that sandwiches and conveys the material to be transferred that is transported by the roller, a registration roller pair that is disposed on the downstream side of the downstream roller pair, and a first drive that rotationally drives the first drive roller A second drive unit that rotationally drives the second drive roller, and a control unit that controls the first drive unit and the second drive unit, the upstream roller pair and the downstream roller pair The transfer material is transferred to the registration roller pair by After being conveyed and reaching the registration roller pair, the first drive unit stops rotating the first drive roller before the second drive unit stops rotating the second drive roller. And an image forming apparatus including the control unit.

  Further, the image forming apparatus further includes a registration driving unit that rotationally drives the registration roller pair, and the control unit reaches the registration roller pair so that the transfer material reaches the registration roller pair, and the first driving roller, the second driving roller, and the After the rotation of the registration roller pair stops, the rotation driving of the first driving roller by the first driving unit is started by the rotation driving of the registration roller pair by the registration driving unit and by the second driving unit. It is preferable to carry out after the start of the rotational drive of the second drive roller.

  Further, it is preferable that the length of the transport path of the transfer material between the upstream roller pair and the registration roller pair is shorter than the length along the transport direction of the transfer material.

  According to the present invention, an upstream roller pair having a driving roller and a driven roller, a downstream roller pair disposed downstream of the upstream roller pair, and a registration roller pair disposed downstream of the downstream roller pair In the image forming apparatus including the image forming apparatus, it is possible to provide an image forming apparatus capable of suppressing slippage of the transfer material on the surface of the driven roller and suppressing uneven wear on the surface of the driven roller.

FIG. 2 is a front view for explaining the arrangement of each component in the printer 1 of the present embodiment. 6 is a schematic diagram illustrating a configuration relating to a first conveyance path L1 between a paper feed cassette 52 and a registration roller pair 80 in the printer 1 of the present embodiment. FIG. 6 is a flowchart illustrating control when the paper T is transported from a paper feed cassette 52 via a registration roller pair 80 in the printer of the present embodiment. 4 is a timing chart corresponding to the flowchart shown in FIG. 3.

Hereinafter, embodiments of an image forming apparatus of the present invention will be described with reference to the drawings.
With reference to FIG. 1, the overall structure of a printer 1 as an image forming apparatus in the present embodiment will be described. FIG. 1 is a front view for explaining the arrangement of components in the printer 1 of the present embodiment.

As shown in FIG. 1, a printer 1 as an image forming apparatus includes an apparatus main body M and an image forming unit GK that forms a predetermined toner image on a sheet T as a sheet-like transfer material based on predetermined image information. And a paper supply / discharge unit KH that supplies the paper T to the image forming unit GK and discharges the paper T on which the toner image is formed.
The outer shape of the apparatus main body M is configured by a case body BD as a casing.

  As shown in FIG. 1, the image forming unit GK includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers (photosensitive members), charging units 10a, 10b, 10c, and 10d, and a laser as an exposure unit. Scanner units 4a, 4b, 4c, 4d, developing devices 16a, 16b, 16c, 16d, toner cartridges 5a, 5b, 5c, 5d, toner supply units 6a, 6b, 6c, 6d, drum cleaning unit 11a, 11b, 11c, 11d, static eliminators 12a, 12b, 12c, 12d, intermediate transfer belt 7, primary transfer rollers 37a, 37b, 37c, 37d, secondary transfer roller 8, counter roller 18, fixing Part 9.

  As shown in FIG. 1, the paper feed / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 64, a conveyance path L for paper T, a registration roller pair 80, a plurality of rollers or roller pairs, A paper unit 50. As will be described later, the transport path L is an aggregate of a first transport path L1, a second transport path L2, a third transport path L3, a manual transport path La, and a return transport path Lb.

Hereinafter, each configuration of the image forming unit GK and the paper supply / discharge unit KH will be described in detail.
First, the image forming unit GK will be described.
In the image forming unit GK, charging by the charging units 10a, 10b, 10c, and 10d in order from the upstream side to the downstream side in order along the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, the laser scanner unit 4a, 4b, 4c, 4d exposure, development devices 16a, 16b, 16c, 16d development, intermediate transfer belt 7 and primary transfer rollers 37a, 37b, 37c, 37d primary transfer, static eliminators 12a, 12b, 12c, 12d Is eliminated, and cleaning is performed by the drum cleaning units 11a, 11b, 11c, and 11d.
In the image forming unit GK, the secondary transfer by the intermediate transfer belt 7, the secondary transfer roller 8 and the counter roller 18, and the fixing by the fixing unit 9 are performed.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is formed of a cylindrical member and functions as a photosensitive member or an image carrier. Each of the photosensitive drums 2 a, 2 b, 2 c, and 2 d is disposed so as to be rotatable in the direction of an arrow about an axis that extends in a direction orthogonal to the traveling direction of the intermediate transfer belt 7. An electrostatic latent image can be formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d.

  Each of the charging units 10a, 10b, 10c, and 10d is disposed to face the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the charging units 10a, 10b, 10c, and 10d uniformly charges the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d negatively (minus polarity) or positively (plus polarity).

  The laser scanner units 4a, 4b, 4c, and 4d function as exposure units, and are spaced apart from the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the laser scanner units 4a, 4b, 4c, and 4d includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  Each of the laser scanner units 4a, 4b, 4c, and 4d scans and exposes the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d based on image information input from an external device such as a PC (personal computer). The scanning exposure is performed by each of the laser scanner units 4a, 4b, 4c, and 4d, thereby removing the charges on the exposed portions of the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Thereby, electrostatic latent images are formed on the respective surfaces of the photosensitive drums 2a, 2b, 2c, and 2d.

  The developing devices 16a, 16b, 16c, and 16d are provided corresponding to the photosensitive drums 2a, 2b, 2c, and 2d, respectively, and are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the developing devices 16a, 16b, 16c, and 16d attaches the toner of each color to the electrostatic latent image formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, and converts the color toner image into the photosensitive drum. 2a, 2b, 2c and 2d are formed on the respective surfaces. Each of the developing devices 16a, 16b, 16c, and 16d corresponds to four colors of yellow, cyan, magenta, and black. Each of the developing devices 16a, 16b, 16c, and 16d includes a developing roller disposed opposite to the surface of the photosensitive drums 2a, 2b, 2c, and 2d, a stirring roller for stirring the toner, and the like.

  Each of the toner cartridges 5a, 5b, 5c, and 5d is provided corresponding to each of the developing devices 16a, 16b, 16c, and 16d, and each color toner supplied to each of the developing devices 16a, 16b, 16c, and 16d. To accommodate. Each of the toner cartridges 5a, 5b, 5c, and 5d accommodates yellow toner, cyan toner, magenta toner, and black toner.

  The toner supply units 6a, 6b, 6c, and 6d are provided corresponding to the toner cartridges 5a, 5b, 5c, and 5d and the developing devices 16a, 16b, 16c, and 16d, respectively. The toners of the respective colors accommodated in 5d are supplied to the developing devices 16a, 16b, 16c, and 16d, respectively. Each of the toner supply units 6a, 6b, 6c, and 6d and each of the developing devices 16a, 16b, 16c, and 16d are connected by a toner supply path (not shown).

  To the intermediate transfer belt 7, the toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred. The intermediate transfer belt 7 is stretched around a driven roller 35, a counter roller 18 including a driving roller, a tension roller 36, and the like. Since the tension roller 36 biases the intermediate transfer belt 7 from the inside to the outside, a predetermined tension is applied to the intermediate transfer belt 7.

  Primary transfer rollers 37a, 37b, 37c, and 37d are arranged to face each other on the side opposite to the photosensitive drums 2a, 2b, 2c, and 2d with the intermediate transfer belt 7 interposed therebetween.

  A predetermined portion of the intermediate transfer belt 7 is sandwiched between the primary transfer rollers 37a, 37b, 37c, and 37d and the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The predetermined portion thus sandwiched is pressed against the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Primary transfer nips N1a, N1b, N1c, and N1d are formed between the photosensitive drums 2a, 2b, 2c, and 2d and the primary transfer rollers 37a, 37b, 37c, and 37d, respectively. In the primary transfer nips N1a, N1b, N1c, and N1d, the respective color toner images developed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially transferred to the intermediate transfer belt 7. As a result, a full-color toner image is formed on the intermediate transfer belt 7.

  The primary transfer rollers 37a, 37b, 37c, and 37d respectively transfer the color toner images formed on the photosensitive drums 2a, 2b, 2c, and 2d to the intermediate transfer belt 7 by a primary transfer bias applying unit (not shown). A primary transfer bias for transferring is applied.

  The static eliminators 12a, 12b, 12c, and 12d are arranged to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The static eliminators 12a, 12b, 12c, and 12d respectively irradiate the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d to irradiate light, and the photosensitive drums 2a, 2b, and 2c after the primary transfer is performed. 2d, each surface is neutralized (charge is removed).

  The drum cleaning units 11a, 11b, 11c, and 11d are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. Each of the drum cleaning units 11a, 11b, 11c, and 11d removes toner and adhering matter remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and conveys the removed toner to a predetermined recovery mechanism. And collect it.

  The secondary transfer roller 8 secondarily transfers the toner image primarily transferred to the intermediate transfer belt 7 onto the paper T. A secondary transfer bias for transferring the full color toner image formed on the intermediate transfer belt 7 to the paper T is applied to the secondary transfer roller 8 by a secondary transfer bias applying unit (not shown).

  The secondary transfer roller 8 contacts or separates from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is configured to be movable between a contact position where the secondary transfer roller 8 is in contact with the intermediate transfer belt 7 and a spaced position where the secondary transfer roller 8 is separated from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is disposed at the contact position when the toner image primarily transferred onto the surface of the intermediate transfer belt 7 is secondarily transferred to the paper T, and is separated at other times. Placed in.

  On the opposite side of the intermediate transfer belt 7 from the secondary transfer roller 8, a counter roller 18 is disposed. A predetermined portion of the intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the opposing roller 18. Then, the paper T is pressed against the outer surface of the intermediate transfer belt 7 (the surface on which the toner image is primarily transferred). A secondary transfer nip N <b> 2 is formed between the intermediate transfer belt 7 and the secondary transfer roller 8. The toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the paper T in the secondary transfer nip N2.

  The fixing unit 9 melts and presses each color toner constituting the toner image secondarily transferred onto the paper T to fix it on the paper T. The fixing unit 9 includes a heating rotator 9a heated by a heater and a pressure rotator 9b pressed against the heating rotator 9a. The heating rotator 9a and the pressure rotator 9b sandwich and pressurize the paper T onto which the toner image has been secondarily transferred, and convey the paper T. By transporting the paper T while being sandwiched between the heating rotator 9a and the pressure rotator 9b, the toner transferred to the paper T is fixed to the paper T by being melted and pressurized. The

Next, the paper supply / discharge unit KH will be described.
As shown in FIG. 1, a paper feed cassette 52 that stores paper T is disposed below the apparatus main body M. The paper feed cassette 52 is configured to be pulled out from the housing of the apparatus main body M in the horizontal direction. In the paper feed cassette 52, a placement plate 60 on which the paper T is placed is disposed. In the paper feed cassette 52, the paper T is stored in a state of being stacked on the placement plate 60. The paper T placed on the placement plate 60 is sent out to the transport path L by the cassette paper feed unit 51 arranged at the end of the paper feed cassette 52 on the paper feed side (the left end in FIG. 1). The cassette paper feeding unit 51 includes a forward feed roller 61 for taking out the paper T on the placement plate 60 and a paper feed roller pair 81 for feeding the paper T one by one to the transport path L. Is provided.

  A manual paper feed unit 64 is provided on the left side surface (left side in FIG. 1) of the apparatus main body M. The manual paper feed unit 64 is provided mainly for supplying the apparatus main body M with a paper T of a size and type different from the paper T set in the paper feed cassette 52. The manual paper feed unit 64 includes a manual feed tray 65 that forms a part of the left side surface of the apparatus main body M in the closed state, and a paper feed roller 66. The lower end of the manual feed tray 65 is attached to the vicinity of the paper feed roller 66 so as to be rotatable (openable and closable). The paper T is placed on the open manual feed tray 65. The paper feed roller 66 feeds the paper T placed on the open manual feed tray 65 to the manual feed path La.

  A paper discharge unit 50 is provided on the upper side of the apparatus main body M. The paper discharge unit 50 discharges the paper T to the outside of the apparatus main body M. Details of the paper discharge unit 50 will be described later.

  The conveyance path L for conveying the paper T includes a first conveyance path L1 from the cassette paper feeding unit 51 to the secondary transfer nip N2, a second conveyance path L2 from the secondary transfer nip N2 to the fixing unit 9, and a fixing unit. 9 to the paper discharge unit 50, the manual conveyance path La for joining the paper supplied from the manual paper feed unit 64 to the first conveyance path L1, and the third conveyance path L3 from the downstream side to the upstream side. And a return conveyance path Lb for reversing the sheet conveyed to the side and returning it to the first conveyance path L1.

Moreover, the 1st junction part P1 and the 2nd junction part P2 are provided in the middle of the 1st conveyance path L1. A first branch portion Q1 is provided in the middle of the third transport path L3.
The first joining part P1 is a joining part where the manual feed path La joins the first transport path L1. The second junction P2 is a junction where the return conveyance path Lb merges with the first conveyance path L1.
The first branch portion Q1 is a branch portion where the return transport path Lb branches from the third transport path L3.

  In the middle of the first conveyance path L1 (specifically, between the second joining portion P2 and the secondary transfer roller 8), a paper detection sensor 850 for detecting the paper T (see FIG. 2; details will be described later). And a registration roller pair 80 for adjusting the timing of skew correction of the paper T and the formation of the toner image in the image forming unit GK. The paper detection sensor 850 is disposed immediately before the registration roller pair 80 in the transport direction of the paper T (upstream in the transport direction). The registration roller pair 80 conveys the paper T by performing the above correction and timing adjustment based on the detection signal information from the paper detection sensor 850.

  An intermediate roller pair 82 is disposed between the first joining portion P1 and the second joining portion P2 in the first transport path L1. The intermediate roller pair 82 is disposed on the downstream side of the paper feed roller pair 81, sandwiches the paper T conveyed from the paper feed roller pair 81, and conveys it to the registration roller pair 80.

  The return conveyance path Lb is a conveyance path that is provided so that the opposite surface (non-printing surface) to the surface that has already been printed faces the intermediate transfer belt 7 when performing duplex printing on the paper T. According to the return transport path Lb, the paper T transported from the first branching section Q1 to the paper discharge section 50 is turned upside down and returned to the first transport path L1 and arranged upstream of the secondary transfer roller 8. It can be conveyed to the upstream side of the pair of registration rollers 80. A predetermined toner image is transferred onto the non-printing surface by the photosensitive drums 2a, 2b, 2c, and 2d on the paper T that has been turned upside down by the return conveyance path Lb.

  A rectifying member 58 is provided in the first branch portion Q1. The rectifying member 58 rectifies the transport direction of the paper T that is carried out of the fixing unit 9 and transports the third transport path L3 from the upstream side toward the downstream side in a direction toward the paper discharge unit 50 and the paper discharge unit 50. The conveyance direction of the paper T that is conveyed from the downstream side toward the upstream side of the third conveyance path L3 is rectified in a direction toward the return conveyance path Lb.

  A paper discharge unit 50 is formed at the end of the third transport path L3. The paper discharge unit 50 is disposed on the upper side of the apparatus main body M. The paper discharge unit 50 opens toward the right side of the apparatus main body M (the right side in FIG. 1). The paper discharge unit 50 includes a discharge roller pair 53. According to the discharge roller pair 53, the paper T conveyed from the upstream side to the downstream side in the third conveyance path L3 is discharged to the outside of the apparatus main body M, and the conveyance direction of the paper T is reversed in the paper discharge unit 50. Thus, the paper T can be transported toward the upstream side of the third transport path L3.

On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the apparatus body M. The paper discharge stacking unit M1 is a part formed by the upper surface of the apparatus main body M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the apparatus main body M. In the paper discharge stacking unit M1, sheets T formed with a predetermined toner image and discharged from the paper discharge unit 50 are stacked and stacked.
A paper detection sensor is disposed at a predetermined position on each conveyance path.

  Hereinafter, with reference to the drawings, a configuration related to a characteristic part in the printer 1 of the present embodiment will be described. FIG. 2 is a schematic diagram showing a configuration relating to the first conveyance path L1 between the paper feed cassette 52 and the registration roller pair 80 in the printer 1 of the present embodiment.

  As shown in FIG. 2, the first conveyance path L1 between the paper feed cassette 52 and the registration roller pair 80 is directed from the paper feed cassette 52 to the registration roller pair 80 (from the upstream side to the downstream side). A forward feed roller 61, a paper feed roller pair 81 as an upstream roller pair, an intermediate roller pair 82 as a downstream roller pair, and a registration roller pair 80 are disposed.

  Further, as described above, the paper detection sensor 850 is disposed immediately before the registration roller pair 80 in the transport direction of the paper T (upstream in the transport direction). The paper detection sensor 850 can detect the presence or absence of the paper T that is conveyed immediately before the registration roller pair 80 by using the reflected light.

  As described above, the paper T stored in the paper feed cassette 52 is sequentially sent out by the forward feed roller 61, the paper feed roller pair 81, and the intermediate roller pair 82, and passes through the first transport path L1 toward the registration roller pair 80. Transport. The first transport path L1 extends upward in the overall view.

  The front feed roller 61 is disposed at the end of the paper feed cassette 52 on the paper feed side (the left end in FIG. 1), and constitutes the cassette paper feed unit 51 together with the paper feed roller pair 81. According to the forward feed roller 61, the paper T placed on the placement plate 60 in the lifted state is taken out from the paper feed cassette 52 and sent out to the transport path L (first transport path L <b> 1).

  The roller shaft 61A of the forward feed roller 61 is directly connected to a forward feed roller driving unit 833 that rotationally drives the forward feed roller 61. The forward feed roller driving unit 833 rotates the forward feed roller 61 at a predetermined speed. Accordingly, the forward feed roller 61 can convey the paper T stored in the paper feed cassette 52 toward the paper feed roller pair 81.

  The paper feed roller pair 81 is disposed on the downstream side of the forward feed roller 61. The paper feed roller pair 81 includes a paper feed drive roller 811 as a first drive roller and a separation roller 812 as a first driven roller. The paper feed drive roller 811 is disposed above the separation roller 812.

  A paper feed roller drive unit 813 as a first drive unit that rotationally drives the paper feed drive roller 811 is directly connected to the roller shaft 811A of the paper feed drive roller 811. The paper feed drive roller 811 is rotationally driven at a predetermined speed by the paper feed roller drive unit 813, and the separation roller 812 is rotated following the rotation of the paper feed drive roller 811. As a result, the paper feed roller pair 81 can sandwich and transport the paper T fed by the forward feed roller 61.

  The separation roller 812 is provided to separate the sheets T fed by the sheet feed driving roller 811 one by one. In other words, the separation roller 812 is provided to prevent double feeding of the paper T (a plurality of papers T are sent out in a state where they are overlapped). The surface (circumferential surface) of the separation roller 812 is formed of a material having a high friction coefficient such as rubber. According to the separation roller 812, the separation roller 812 uses the height of the friction coefficient to come into contact with the paper T from the side opposite to the paper feed driving roller 811 and when the paper T is likely to be double-fed, the separation roller 812 It is possible to prevent the paper T in contact with 812 from being sent out.

  The separation roller 812 includes a torque limiter (not shown) on the roller shaft 812A. When the paper T does not exist between the paper feed driving roller 811 and the separation roller 812 and both the rollers 811 and 812 are in contact, or when only one paper T enters between the two rollers 811 and 812 The separation roller 812 is applied with a torque that is greater than the torque limiter set torque. In that case, the separation roller 812 rotates in the direction of feeding the paper T to the downstream side in accordance with the rotation of the paper feed driving roller 811.

  On the other hand, when a plurality of sheets T enter with the paper T overlapped between the paper feed drive roller 811 and the separation roller 812 (when the paper T is fed in a double manner), the torque applied to the separation roller 812 is the torque limiter's torque. The set torque is not exceeded. In that case, the paper T on the separation roller 812 side of the paper T in a state where the contact surface with the paper feed drive roller 811 moves in the opposite direction to the surface of the paper feed drive roller 811, that is, the overlapped paper T The separation roller 812 rotates in the direction to return to the paper feed cassette 52. Thereby, since the paper T on the separation roller 812 side is suppressed from being fed out from the pair of paper feed rollers 81, the double feeding of the paper T can be suppressed.

  The intermediate roller pair 82 is disposed on the downstream side of the paper feed roller pair 81. The intermediate roller pair 82 includes an intermediate drive roller 821 as a second drive roller and an intermediate driven roller 822 as a third roller. The intermediate driving roller 821 is disposed above the intermediate driven roller 822. The intermediate roller pair 82 sandwiches and conveys the paper T conveyed by the paper feed roller pair 81.

  The roller shaft 821A of the intermediate drive roller 821 is directly connected to an intermediate roller drive unit 823 as a second drive unit that rotationally drives the intermediate drive roller 821. The intermediate roller driving unit 823 rotates the intermediate driving roller 821 at a predetermined speed, and the intermediate driven roller 822 is rotated by the rotation of the intermediate driving roller 821. As a result, the intermediate roller pair 82 can sandwich and transport the paper T fed by the paper feed roller pair 81.

  The registration roller pair 80 is disposed on the downstream side of the intermediate roller pair 82. The registration roller pair 80 includes a registration driving roller 801 composed of a driving roller and a registration driven roller 802 composed of a driven roller.

  A registration driving unit 803 that rotates the registration driving roller 801 is directly connected to the roller shaft 801A of the registration driving roller 801. The registration driving unit 803 rotates the registration driving roller 801 at a predetermined speed, and the registration driven roller 802 is rotated by the rotation of the registration driving roller 801. As a result, the registration roller pair 80 can synchronize with the skew correction of the paper T sent out by the intermediate roller pair 82 and the formation of the toner image in the image forming unit GK.

The control unit 840 controls the forward feed roller driving unit 833, the paper feed roller driving unit 813, the intermediate roller driving unit 823, the registration driving unit 803, and the like.
The control unit 840 rotates the paper feed driving roller 811 by the paper feed roller driving unit 813 after the paper T is conveyed to the registration roller pair 80 by the paper feed roller pair 81 and the intermediate roller pair 82 and reaches the registration roller pair 80. The driving is stopped before the intermediate roller driving unit 823 stops the rotation of the intermediate driving roller 821.

Further, the control unit 840 drives the paper feed roller after the paper T reaches the registration roller pair 80 and rotation of the paper feed drive roller 811, the intermediate drive roller 821 and the resist roller pair 80 (registration drive roller 801) stops. The rotation driving of the sheet feed driving roller 811 by the unit 813 is performed after the rotation driving of the registration roller pair 80 by the registration driving unit 803 and the rotation driving of the intermediate driving roller 821 by the intermediate roller driving unit 823 are started.
The control of driving of the driving units 803, 813, 823, and 833 by the control unit 840 will be described in detail later.

A first junction P <b> 1 is disposed between the paper feed roller pair 81 and the intermediate roller pair 82. Between the intermediate roller pair 82 and the registration roller pair 80, a second joining portion P2 is disposed.
The length of the transport path of the paper T between the paper feed roller pair 81 and the registration roller pair 80 is shorter than the length along the transport direction of the paper T.

Next, the operation of the printer 1 of the present embodiment will be briefly described with reference to FIG.
First, a case where single-sided printing is performed on the paper T stored in the paper feed cassette 52 will be described.
The paper T accommodated in the paper feed cassette 52 is sent out to the first transport path L1 by the forward feed roller 61 and the paper feed roller pair 81, and then intermediated via the first joining portion P1 and the first transport path L1. It is conveyed to the registration roller pair 80 by the roller pair 82.
In the registration roller pair 80, skew correction of the paper T and timing adjustment with the toner image are performed.

The paper T discharged from the registration roller pair 80 is introduced between the intermediate transfer belt 7 and the secondary transfer roller 8 (secondary transfer nip N2) via the first conveyance path L1. A toner image is transferred onto the paper T between the intermediate transfer belt 7 and the secondary transfer roller 8.
Thereafter, the paper T is discharged from between the intermediate transfer belt 7 and the secondary transfer roller 8, and is interposed between the heating rotator 9a and the pressure rotator 9b in the fixing unit 9 via the second conveyance path L2. Introduced into the fixing nip. Then, the toner melts in the fixing nip, and the toner is fixed on the paper T.

Next, the paper T is transported to the paper discharge unit 50 through the third transport path L3, and is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1 by the discharge roller pair 53.
In this way, single-sided printing of the paper T stored in the paper feed cassette 52 is completed.

  When single-sided printing is performed on the paper T placed on the manual feed tray 65, the paper T placed on the manual feed tray 65 is sent out to the manual feed path La by the paper feed roller 66, and then the first joining portion. It is conveyed to the registration roller pair 80 via P1 and the first conveyance path L1. Subsequent operations are the same as the one-side printing operation of the paper T accommodated in the paper feed cassette 52 described above, and a description thereof will be omitted.

Next, the operation of the printer 1 when performing duplex printing will be described.
In the case of single-sided printing, as described above, the paper T on which single-sided printing has been performed is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1, and the printing operation is completed.
On the other hand, when performing double-sided printing, the paper T on which single-sided printing has been performed is reversed from the time of single-sided printing and conveyed again to the registration roller pair 80 via the return conveyance path Lb. Then, double-sided printing is performed on the paper T.

  More specifically, the operation is the same as the above-described single-sided printing operation until the paper T on which single-sided printing has been performed is discharged from the paper discharge unit 50 by the discharge roller pair 53. Thus, in the case of double-sided printing, in a state where the paper T on which single-sided printing has been performed is held by the discharge roller pair 53, the rotation of the discharge roller pair 53 is stopped and rotated in the reverse direction. When the discharge roller pair 53 is thus rotated in the reverse direction, the paper T held by the discharge roller pair 53 moves in the reverse direction (the direction from the paper discharge unit 50 toward the first branching unit Q1) along the third conveyance path L3. ).

  As described above, when the paper T is transported in the reverse direction on the third transport path L3, the paper T is rectified to the return transport path Lb by the rectifying member 58, and then, via the second junction P2. Then, it joins the first transport path L1. Here, the paper T is turned upside down from the one-side printing.

  Further, the paper T is subjected to the correction or the adjustment by the registration roller pair 80 and is introduced between the photosensitive drum 2 and the secondary transfer roller 8 through the first conveyance path L1. Since the non-printing surface of the paper T passes through the return conveyance path Lb, the non-printing surface faces the photosensitive drum 2, so that the toner image is transferred to the non-printing surface, and as a result, duplex printing is performed.

  Next, the operation of the control unit 840 that is a characteristic part of the printer 1 of the present embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing control when the paper T is conveyed from the paper feed cassette 52 through the registration roller pair 80 in the printer of this embodiment. FIG. 4 is a timing chart corresponding to the flowchart shown in FIG.

  In the printer 1 of the first embodiment, when the printer 1 is turned on, the charging unit 10, the laser scanner unit 4, the developing device 16, the counter roller 18, the secondary transfer roller 8, and the printer control unit (see FIG. (Not shown), power is supplied to the fixing unit 9 and the like, and the charging unit 10, the laser scanner unit 4, the developing device 16, the counter roller 18, the secondary transfer roller 8 and the fixing unit 9 are controlled by a control signal from the printer control unit. Are controlled respectively. Then, the charging process, the exposure process, the development process, the transfer process, and the fixing process are sequentially performed.

Prior to the transfer process, primary paper feeding is started. The primary paper feed is a paper feed in which the paper T stored in the paper feed cassette 52 is conveyed to the registration roller pair 80.
Specifically, in the paper feed cassette 52, the placement plate 60 is lifted so that the leading end portion (downstream end portion) of the paper T rises. As a result, the paper T comes into contact with the forward feed roller 61.
In this state, in step ST1, the control unit 840 controls the drive of the forward feed roller drive unit 833 so that the rotational drive of the forward feed roller 61 is started. As a result, the forward feed roller 61 is rotationally driven, and the paper T is sent out toward the paper feed roller pair 81.

Next, in step ST2, the control unit 840 starts the rotation of the paper feed drive roller 811 and the intermediate roller drive unit 823 simultaneously (see FIG. 4), so that the paper feed roller drive unit 813 and the intermediate roller drive unit 823 are started. Control the drive. Here, the rotation of the registration roller pair 80 is stopped without being started. That is, the control unit 840 does not rotate the registration roller pair 80 by the registration driving unit 803.
In FIG. 4, “ON” means a state where each drive roller is rotationally driven, and “OFF” means a state where each drive roller is not rotationally driven (stopped). means.

  More specifically, the control unit 840 rotates the paper feed drive roller 811 by starting the drive of the paper feed roller drive unit 813. As a result, the paper T fed from the forward feed roller 61 is delivered to the paper feed roller pair 81. The separation roller 81b rotates following the paper feed drive roller 811 when no double feed occurs, and performs a predetermined double feed prevention operation when no double feed occurs. Thereafter, the paper feed roller pair 81 sends the paper T toward the intermediate roller pair 82.

  Further, the control unit 840 rotates the intermediate drive roller 821 by starting the drive of the intermediate roller drive unit 823 at the same timing as the drive of the paper feed roller drive unit 813 (see FIG. 4). Further, the intermediate driven roller 822 rotates following the rotation of the intermediate drive roller 821. As a result, the paper T sent out from the paper feed roller pair 81 is delivered to the intermediate roller pair 82. Thereafter, the intermediate roller pair 82 sends the paper T toward the registration roller pair 80.

  In step ST 3, the paper T sent out by the intermediate roller pair 82 reaches the registration roller pair 80. Here, the leading end portion of the paper T abuts against a registration nip N8 between the registration driving roller 801 and the registration driven roller 802 in the registration roller pair 80. The registration roller pair 80 (registration driving roller 801) is not driven to rotate, so that the sheet T is bent and skew correction is performed.

  In step ST <b> 4, the control unit 840 stops driving the paper feed roller drive unit 813 and stops the rotational drive of the paper feed drive roller 811. Thereby, the bending of the paper T between the paper feed roller pair 81 and the intermediate roller pair 82 is reduced.

In step ST5, the control unit 840 stops the driving of the intermediate roller driving unit 823 after a predetermined time (Δt1) has elapsed from the stop of the rotation driving of the paper feed driving roller 811, and stops the rotational driving of the intermediate driving roller 821. (See FIG. 4).
The predetermined time (Δt1) from the stop of the rotation drive of the paper feed drive roller 811 to the stop of the rotation drive of the intermediate drive roller 821 is appropriately set, but is preferably 20 to 30 ms.
In this way, the primary paper feed is completed.

Next, secondary paper feeding is started. The secondary paper feeding refers to paper feeding in which the paper T on which skew correction or the like has been performed in the registration roller pair 80 is conveyed to the secondary transfer nip N2.
In step ST6, the control unit 840 starts driving the registration driving unit 803 and rotates the registration roller pair 80 (registration driving roller 801).
Further, the control unit 840 starts driving the intermediate roller driving unit 823 at the same timing as the start of driving the registration roller pair 80 (see FIG. 4), and rotates the intermediate driving roller 821.
Due to the rotation of the registration roller pair 80 and the intermediate drive roller 821, the sheet T on which skew correction or the like has been performed in the registration roller pair 80 is transferred from the registration roller pair 80 to the secondary transfer nip N2 (the intermediate transfer belt 7 and the secondary transfer belt 7). (To the transfer roller 8).

In step ST7, after a predetermined time (Δt2) has elapsed from the start of driving of the registration roller pair 80 (and the intermediate drive roller 821), the drive of the paper feed roller drive unit 813 is started and the drive of the paper feed drive roller 811 is rotated. Start.
The predetermined time (Δt2) from the start of the rotational drive of the registration roller pair 80 to the start of the rotational drive of the paper feed drive roller 811 is appropriately set, but is preferably 20 to 30 ms.
Note that the rotation driving of the registration roller pair 80 and the paper driving roller 811 may be started at the same time.

  A predetermined transfer process is performed on the paper T that has reached the secondary transfer nip N2. Then, the paper T onto which the toner image has been transferred in the transfer process is conveyed toward the fixing unit 9 through the second conveyance path L2.

  In the fixing unit 9, heat is applied to the toner adhering to the paper T passing between the heating rotator 9a and the pressure rotator 9b through the heating rotator 9a, and the toner is dissolved by this heat. At the same time, the toner image is fixed on the paper T by applying pressure to the paper T by the pressure rotator 9b.

According to the printer 1 of the present embodiment, the following effects are exhibited.
In the printer 1 of the present embodiment, the control unit 840 controls the paper feed roller drive unit 813 and the intermediate drive roller 821, and the paper T is conveyed to the registration roller pair 80 by the paper feed roller pair 81 and the intermediate roller pair 82. Then, after reaching the registration roller pair 80, the rotation of the paper feed drive roller 811 by the paper feed roller drive unit 813 is stopped before the rotation drive of the intermediate drive roller 821 by the intermediate roller drive unit 823 is stopped. Part 840.

  Therefore, the bending of the paper T is unlikely to occur between the paper feed roller pair 81 and the intermediate roller pair 82, and thereby the load applied to the surface of the separation roller 812 is not easily reduced. As a result, the slippage of the paper T is less likely to occur on the surface of the separation roller 812, and uneven wear is less likely to occur on the surface of the separation roller 812. Therefore, the effect of preventing the double feeding of the paper T by the separation roller 812 is likely to be sustained.

  In this embodiment, the control unit 840 drives the paper feed roller after the paper T reaches the registration roller pair 80 and the paper feed drive roller 811, the intermediate drive roller 821, and the registration roller pair 80 stop rotating. The rotation driving of the paper feed driving roller 811 by the unit 813 is performed after the rotation driving of the registration roller pair 80 by the registration driving unit 803 and the rotation driving of the intermediate driving roller 821 by the intermediate driving roller 821 are started.

  Therefore, the sheet T is not bent between the paper feed roller pair 81 and the intermediate roller pair 82, and the load applied to the surface of the separation roller 812 is thereby stabilized. As a result, the slippage of the paper T is less likely to occur on the surface of the separation roller 812, and uneven wear is less likely to occur on the surface of the separation roller 812. Therefore, the effect of preventing the double feeding of the paper T by the separation roller 812 is likely to be sustained.

As mentioned above, although preferred embodiment of this invention was described, this invention can be implemented with a various form, without being limited to embodiment mentioned above.
For example, the third roller in the downstream roller pair is the intermediate driven roller 822 that is a driven roller in the embodiment, but is not limited thereto, and may be a driving roller.

The embodiment is a so-called indirect transfer type image forming apparatus, and the transfer nip is formed as the secondary transfer nip N2 between the intermediate transfer belt and the secondary transfer roller, but is not limited thereto. For example, in the case of a direct transfer type image forming apparatus, the transfer nip is formed, for example, between a photosensitive drum and a transfer roller.
The type of the image forming apparatus of the present invention is not particularly limited, and may be a copier, a printer, a facsimile, or a complex machine thereof.
The sheet-shaped transfer material is not limited to paper, and may be a film sheet, for example.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photosensitive drum (image carrier), 16 ... Developing device, 9 ... Fixing unit, 80 ... Registration roller pair, 81 ... Paper feed roller pair (Upstream) Side roller pair), 82... Intermediate roller pair (downstream roller pair), 803... Registration drive unit, 811... Paper feed drive roller (first drive roller), 812. Roller), 813... Feed roller driving section (first driving section), 821... Intermediate driving roller (second driving roller), 822... Intermediate driven roller (third roller), 823. Drive unit (second drive unit), 840 ... control unit, T ... paper (transfer material)

Claims (3)

A pair of upstream rollers having a first drive roller and a first driven roller and conveying a sheet-shaped transfer material sandwiched between the first drive roller and the first driven roller;
It is arranged downstream of the upstream roller pair, has a second drive roller and a third roller, and is conveyed by the upstream roller pair between the second drive roller and the third roller. A pair of downstream rollers for nipping and conveying the transferred material;
A registration roller pair disposed downstream of the downstream roller pair;
A first drive unit that rotationally drives the first drive roller;
A second drive unit that rotationally drives the second drive roller;
A control unit for controlling the first driving unit and the second driving unit, wherein the transfer material is conveyed to the registration roller pair by the upstream roller pair and the downstream roller pair, and is transferred to the registration roller pair; A controller that stops rotation of the first drive roller by the first drive unit before reaching stop of rotation of the second drive roller by the second drive unit after reaching the first drive unit. Image forming apparatus. A registration driving unit for rotating the registration roller pair;
The controller is configured so that the transfer material reaches the registration roller pair, and after the rotation of the first drive roller, the second drive roller, and the registration roller pair is stopped, the first drive unit The rotation driving of the first driving roller is started after the rotation driving of the registration roller pair by the registration driving unit and the rotation driving of the second driving roller by the second driving unit are started. The image forming apparatus described in 1. The image forming apparatus according to claim 1, wherein a length of a conveyance path of the transfer material between the upstream roller pair and the registration roller pair is shorter than a length along a conveyance direction of the transfer material. .

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