Feeding device and feeding method, and image forming device Number:7,395,025 from the United States Patent and Trademark Office (PTO) owispatent

Title: Feeding device and feeding method, and image forming device

Abstract: A paper transporting apparatus transporting continuous paper to a paper processing part that performs designated processing on the continuous paper includes a drive roller that transports the continuous paper in a forward direction with respect to the paper processing part and a direction opposite to the forward direction by a frictional force, a pre-centering mechanism, disposed upstream of the drive roller with respect to the forward direction, that regulates a position of the continuous paper with respect to the forward direction and a direction orthogonal to the forward direction by abutting against the continuous paper, and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the forward direction, that increases tension on the continuous paper.

Patent Number: 7,395,025 Issued on 07/01/2008 to Matsuzuki,   et al.

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Inventors:	Matsuzuki; Masato (Kawasaki, JP), Ishida; Shigeo (Kawasaki, JP)
Assignee:	Fuji Xerox Co., Ltd. (Tokyo, JP)
Appl. No.:	10/483,065
Filed:	July 23, 2001
PCT Filed:	July 23, 2001
PCT No.:	PCT/JP01/06358
371(c)(1),(2),(4) Date:	January 07, 2004
PCT Pub. No.:	WO03/010080
PCT Pub. Date:	February 06, 2003

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Current U.S. Class:	399/384 ; 399/388; 399/395; 400/578; 400/579; 400/611; 400/613
Current International Class:	G03G 15/00 (20060101); B41J 15/04 (20060101); B41J 15/16 (20060101); B65H 23/00 (20060101)
Field of Search:	399/384

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References Cited [Referenced By]

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U.S. Patent Documents

3653757	April 1972	Newcomb
3800992	April 1974	Yamagishi
4496955	January 1985	Maeyama et al.
4819024	April 1989	Kagayama et al.
4838719	June 1989	Une
4919318	April 1990	Wong
4961089	October 1990	Jamzadeh
5008710	April 1991	Kobayashi et al.
5172989	December 1992	Imaseki et al.
5259307	November 1993	Bourgeois et al.
5337944	August 1994	Shiba
5499093	March 1996	Aerens et al.
5685471	November 1997	Taubenberger
5774777	June 1998	Ohtsuka et al.
5970304	October 1999	Stemmle
6104907	August 2000	Obata et al.
6357349	March 2002	Tomberlin et al.
6412992	July 2002	Mogi
6650864	November 2003	Miyamoto et al.
6659006	December 2003	Brennan et al.
6668716	December 2003	Tsuruta et al.
6673220	January 2004	Voutsas et al.
6763220	July 2004	Nakazawa
6799507	October 2004	Ohba et al.
6922205	July 2005	Mogi
6969206	November 2005	Iwanaga et al.
2003/0039496	February 2003	Miyamoto et al.
2003/0185608	October 2003	Miyamoto et al.
2004/0175213	September 2004	Matsuzuki et al.

Foreign Patent Documents

	A 58-89387		May., 1983		JP
	A 2-152840		Jun., 1990		JP
	A 11-189355		Jul., 1999		JP
	A 11-349191		Dec., 1999		JP
	A 2000-178639		Jun., 2000		JP

Primary Examiner: Colilla; Daniel J.
Assistant Examiner: Ha; Wynn' Q
Attorney, Agent or Firm: Oliff & Berridge PLC

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Claims

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What is claimed is:

1. A paper transporting apparatus transporting continuous paper to a paper processing part that performs designated processing on the continuous paper, comprising: a drive roller that transports the continuous paper in a forward direction with respect to the paper processing part and a direction opposite to the forward direction by a frictional force; a pre-centering mechanism, disposed upstream of the drive roller with respect to the forward direction, that regulates a position of the continuous paper with respect to a direction orthogonal to the forward direction and the backward direction by abutting against the continuous paper; and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the forward direction, that increases tension on the continuous paper, wherein the tension increasing mechanism includes a roller that rotates in the forward direction at a circumferential speed slower than a transport speed of the drive roller when the drive roller transports the continuous paper in the forward direction, and that rotates in the backward direction at a circumferential speed faster than the transport speed of the drive roller when the drive roller transports the continuous paper in the backward direction.

2. A paper transporting apparatus transporting continuous paper to a paper processing part that performs designated processing on the continuous paper, comprising: a drive roller that transports the continuous paper in a forward direction with respect to the paper Processing part and a direction opposite to the forward direction by a frictional force; a pre-centering mechanism, disposed upstream of the drive roller with respect to the forward direction, that regulates a position of the continuous paper with respect to a direction orthogonal to the forward direction and the backward direction by abutting against the continuous paper; and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the forward direction, that increases tension on the continuous paper, wherein the pre-centering mechanism includes: a guide part that abuts against an edge of the continuous paper to regulate its position; and a skew roller, provided at a designated angle with respect to the guide part, that energizes the continuous paper so as to press the continuous paper against the guide part when the continuous paper is transported in the forward direction and the backward direction, the designated angle being set variable.

3. A paper transport method comprising the steps of: driving a drive roller that nips continuous paper together with plural driven rollers and transports the continuous paper to a paper processing part performing designated processing on the continuous paper by a frictional force in a forward direction and a direction opposite to the forward direction; increasing tension on the continuous paper when the continuous paper is transported via a tension increasing mechanism provided upstream of a pre-centering mechanism with respect to the forward direction, wherein the pre-centering mechanism is disposed upstream of the drive roller with respect to the forward direction and regulates the position of the continuous paper with respect to a direction orthogonal to the forward direction and the backward direction by abutting against the continuous paper; and controlling one of the driving step and the increasing step so that a relation of W>U>W/N holds, where W is a transport force by the drive roller, N is the number of the driven rollers, and U is a paper load force by the tension increasing mechanism.

4. The paper transport method according to claim 3, wherein the control step controls the driving step and/or the increasing step so that A/L is 1.0 or more, where A is a distance between a portion of the pre-centering mechanism abutting against the continuous paper and the drive roller, and L is a width of the continuous paper.

5. The paper transport method according to claim 3, wherein the tension increasing mechanism includes a roller, and the increasing step rotates the roller of the tension increasing mechanism at a rotation speed slower than a rotation speed of the drive roller when the continuous paper is transported to the paper processing part.

6. The paper transport method according to claim 3, wherein the tension increasing mechanism includes a roller, and the increasing step rotates the roller of the tension increasing mechanism at a rotation speed faster than the rotation speed of the drive roller when the continuous paper is transported in a direction opposite to the paper processing part.

7. The paper transporting apparatus according to claim 1, wherein the pre-centering mechanism includes: a guide part that abuts against an edge of the continuous paper to regulate its position; and a skew roller, provided at a designated angle with respect to the guide part, that energizes the continuous paper so as to press the continuous paper against the guide part when the continuous paper is transported in the forward direction and the backward direction, the designated angle being set variable.

8. A paper transport method comprising the steps of: driving a drive roller that nips continuous paper together with plural driven rollers and transports the continuous paper to a paper processing part performing designated processing on the continuous paper by a frictional force in a forward direction and a direction opposite to the forward direction; increasing tension on the continuous paper when the continuous paper is transported in the forward direction and the backward direction via a tension increasing mechanism provided upstream of a pre-centering mechanism with respect to the forward direction, wherein the pre-centering mechanism is disposed upstream of the drive roller with respect to the forward direction and regulates the position of the continuous paper with respect to a direction orthogonal to the forward direction and the backward direction by abutting against the continuous paper; and controlling one of the driving step and the increasing step so that a relation of W>U>W/N holds, where W is a transport force by the drive roller, N is the number of the driven rollers, and U is a paper load force by the tension increasing mechanism.

9. An image forming apparatus comprising: an image forming part that forms a designated image on continuous paper; a drive roller that transports the continuous paper to the image forming part by a frictional force; a pre-centering mechanism that is disposed upstream of the drive roller with respect to a transport direction and regulates a position of the continuous paper with respect to a direction orthogonal to the transport direction by abutting against an edge of the continuous paper extending lengthwise; and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the transport direction, that increases tension on the continuous paper, wherein the drive roller transports the continuous paper in a forward direction with respect to the image forming part and a direction opposite to the forward direction, and wherein the tension increasing mechanism includes a roller that rotates in the forward direction at a circumferential speed slower than a transport speed of the drive roller when the drive roller transports the continuous paper in the forward direction, and that rotates in the backward direction at a circumferential speed faster than the transport speed of the drive roller when the drive roller transports the continuous paper in the backward direction.

10. An image forming apparatus comprising: an image forming part that forms a designated image on continuous paper; a drive roller that transports the continuous paper to the image forming part by a frictional force; a pre-centering mechanism that is disposed upstream of the drive roller with respect to a transport direction and regulates a position of the continuous paper with respect to a direction orthogonal to the transport direction by abutting against an edge of the continuous paper extending lengthwise; and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the transport direction, that increases tension on the continuous paper, wherein the drive roller transports the continuous paper in a forward direction with respect to the image forming part and a direction opposite to the forward direction, and wherein the pre-centering mechanism includes: a guide part that abuts against an edge of the continuous paper to regulate its position; and a skew roller, provided at a designated angle with respect to the guide part, that energizes the continuous paper so as to press the continuous paper against the guide part when the continuous paper is transported in the forward direction and the backward direction, the designated angle being set variable.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transporting apparatus and method. The present invention is suitable for a transport mechanism of a pinless printer transporting continuous paper having no feed pins (or tractor pins). The continuous paper here falls into two categories: paper folded back at perforations formed per given length, and a continuous roll of paper.

2. Description of Related Art

Conventional continuous paper is formed with sprocket holes serving as through holes at side edges provided separably from a main body used as a printable area. The continuous paper is transported while feed pins of a paper transport system of a printer are engaging in the sprocket holes. Although such continuous paper has the advantage of being transported in a transport direction without being skewed or becoming slack, it takes processing costs to form through holes at both side edges. Furthermore, since the both side edges are unusable for printing, they must be separated at the termination of printing, leaving dust behind. For this reason, there are demands for the use of continuous paper having no holes at the both side edges. In this case, however, technologies are required for transporting the continuous paper in the transport direction without being skewed or becoming slack.

In a transport mechanism disclosed by Japanese Translation of Unexamined PCT Appln. No. 507666/1997, a paper position regulation unit is provided that presses one edge of holeless continuous paper against a stopper to regulate the position of the continuous paper with respect to a direction orthogonal to a transport direction, and a tension increasing unit and an accumulator are disposed at the following stage of the paper position regulation unit with respect to the transport direction (forward direction). The tension increasing unit, which is made up of a vacuum brake, increases tension on the paper to prevent swing or paper skew in the direction orthogonal to the transport direction of the paper. The accumulator, which is made up of a roller moving vertically, increases tension on the paper to remove slack in the paper in a back feed operation for transporting the paper in a direction opposite to the transport direction (forward direction) during printing. The paper is transported in the forward direction and the backward direction by a drive roller provided at the following stage of the accumulator with respect to the transport direction.

Since printers have been sped up, paper overruns several inches when it stops, and the paper must be run preparatorily several inches when printing is started. Accordingly, when printing is stopped and restarted, a back feed is performed to pull back the paper in the backward direction by the sum of the distances of the overrun and the preparatory run, thereby preventing an excessive space between an image printed previously and the next image to be printed. To stabilize the run of the high-speed printers during paper activation, a back feed amount must be increased to drop activation acceleration. This is because a high activation acceleration leaves inertia in a motor for driving a following drive roller and disables quick transition to a constant speed.

The above-described patent application has several problems. Specifically, (1) the separate arrangement of the tension increasing unit and the accumulator increases the size and cost of the transport mechanism. (2) Since the accumulator removes slack in the paper by vertical movement of the roller, large slack in the paper would increase the distance of vertical movement of the accumulator. Accordingly, if a back feed amount is increased to cope with the speedup of printers, a space for the vertical movement of the accumulator must be allocated in the apparatus, increasing the size of the apparatus. (3) Since vertical movement of the accumulator causes vertical changes in the transport direction, the paper is easily skewed and runs unstably. (4) The vacuum brake is susceptible to wear. Since the vacuum brake applies brake force in accordance with the width of the paper, a different brake force is applied for a different paper width. Therefore, for different paper types, the vacuum brake cannot always apply desired brake forces. (5) Since the tension increasing unit is disposed at the following stage of the paper position regulation unit with respect to the transport direction, paper slack occurring between the paper position regulation unit and the tension increasing unit cannot be removed. (6) Since the tension increasing unit must press a paper edge against the stopper so as not to crush (buckle) it, it is difficult to adjust press forces. Paper buckling limitations limit the types of usable paper. In other words, such a tension increasing mechanism is unsuitable for treating thin paper.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a paper transporting apparatus and method that can achieve paper run stability during transport and the miniaturization and cost reduction of the apparatus with a relatively simple construction, and an image forming apparatus having the paper transporting apparatus.

According to an aspect of the present invention, the paper transporting apparatus transports continuous paper to a paper processing part that performs designated processing on the continuous paper, wherein the paper transporting apparatus includes a drive roller that transports the continuous paper in a forward direction with respect to the paper processing part and a direction opposite to the forward direction by a frictional force, a pre-centering mechanism, disposed upstream of the drive roller with respect to the forward direction, that regulates a position of the continuous paper with respect to the forward direction and a direction orthogonal to the forward direction by abutting against the continuous paper, and a tension increasing mechanism, disposed upstream of the pre-centering mechanism with respect to the forward direction, that increases tension on the continuous paper. Since the paper transporting apparatus has the tension increasing mechanism provided upstream of the pre-centering mechanism, slack in the continuous paper between the tension increasing mechanism and the drive roller can be removed.

Alternatively, the tension increasing mechanism may increase tension on the continuous paper when the drive roller transports the continuous paper in the forward direction and the backward direction. Since the tension increasing mechanism has both the function for increasing tension when the continuous paper is transported in the forward direction, and the function for increasing tension when the continuous paper is transported in the backward direction, more contribution can be made to the miniaturization and cost reduction of the apparatus than when a different tension increasing mechanism is provided for each of the both transport directions.

The tension increasing mechanism may include a roller that rotates in the forward direction at a circumferential speed slower than a transport speed of the drive roller when the drive roller transports the continuous paper in the forward direction, and that rotates in the backward direction at a circumferential speed faster than the transport speed of the drive roller when the drive roller transports the continuous paper in the backward direction. Tension can be increased by speeding up the downstream roller in a direction in which the paper is transported.

The pre-centering mechanism may include a guide part that abuts against an edge of the continuous paper to regulate its position, and a skew roller, provided on the skew by a designated angle with respect to the guide part, that energizes the continuous paper so as to press the continuous paper against the guide part when the continuous paper is transported in the forward direction and the backward direction, the designated angle being set variable. Since the designated angle is variable, the pre-centering mechanism can center the continuous paper in any of the transport direction of the continuous paper, the forward direction, and the backward direction.

According to another aspect of the present invention, the paper transporting apparatus transports continuous paper to a paper processing part that performs designated processing on the continuous paper, wherein the paper transporting apparatus includes a drive roller that transports the continuous paper to the paper processing part by a frictional force, and a skew roller, disposed upstream of the drive roller with respect to a transport direction toward the paper processing part from the drive roller, and on the skew by a variable angle with respect to the transport direction, that energizes the continuous paper while changing the angle so as to converge swing of the continuous paper with respect to a direction orthogonal to the transport direction to zero, wherein a distance between the drive roller and the designated position is greater than a distance between the paper processing part and the drive roller. The paper transporting apparatus regulates the swing of the continuous paper with respect to a direction orthogonal to the transport direction by a frictional force by the skew roller without pressing the continuous paper against a stopper and the like. Therefore, the buckling (crush) of the continuous paper can be prevented. Since a designated angle of the skew roller is variable, the continuous paper can be precisely positioned to reduce the fluctuation of the continuous paper in the paper processing part. Position regulation control can be achieved by a detection part that detects the position of the continuous paper with respect to the orthogonal direction, and a control part that controls change of the designated angle based on a detection result of the detection part.

An image forming apparatus having the above-described paper transport apparatus also constitutes another aspect of the present invention. This image forming apparatus also has the function of the above-described paper transporting apparatus.

A paper transport method as another aspect of the present invention includes the steps of: driving a drive roller that nips continuous paper together with plural driven rollers and transports the continuous paper to a paper processing part performing designated processing on the continuous paper by a frictional force in a forward direction and a direction opposite to the forward direction; increasing tension on the continuous paper when the continuous paper is transported via a tension increasing mechanism provided upstream of a pre-centering mechanism with respect to the forward direction, wherein the pre-centering mechanism is disposed upstream of the drive roller with respect to the forward direction and regulates the position of the continuous paper with respect to the forward direction and a direction orthogonal to the forward direction by abutting against the continuous paper; and controlling the driving step and/or the increasing step so that a relation of W>U>W/N holds, where W is a transport force by the drive roller, N is the number of the driven rollers, and U is a paper load force by the tension increasing mechanism. This method also has the same function as the above-described apparatus. Particularly, the above-described relational expression makes it possible to remove minor slack generated in the continuous paper due to disturbance in cooperation between the drive roller and the tension increasing mechanism.

When a distance between a portion of the pre-centering mechanism abutting against the continuous paper and the drive roller is A, and a width of the continuous paper is L, the control step may control the driving step or the increasing step so that A/L is 1.0 or more. This method also has the same function as the above-described apparatus. Particularly, the above-described relational expression makes it possible to promote automatic correction on slack by the drive roller. As described above, tension can be increased by speeding up a roller downstream with respect to the direction in which the paper is transported.

A transport method as another aspect of the present invention includes the steps of: driving a drive roller that nips continuous paper together with plural driven rollers and transports the continuous paper to a paper processing part performing designated processing on the continuous paper by a frictional force; driving a skew roller, disposed upstream of the drive roller with respect to a transport direction toward the paper processing part from the drive roller, and on the skew by a variable angle with respect to the transport direction, that energizes the continuous paper to regulate the position of the continuous paper with respect to a direction orthogonal to the transport direction; detecting the position of the continuous paper with respect to the orthogonal direction; and controlling change of the angle so as to converge swing of the continuous paper with respect to the orthogonal direction to zero based on a result of the detecting step. This transport method also has the same function as the above-described paper transporting apparatus.

Other characteristics of the present invention will be made apparent by embodiments described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail based on the followings, wherein:

FIG. 1 is a sectional view of a printer of a first embodiment of the present invention;

FIG. 2 is a schematic sectional view showing the neighborhood of a drive roller of the printer shown in FIG. 1;

FIG. 3 is a schematic plan view showing a portion from a back tension roller to a drive roller for explaining the removal of slack in continuous paper by the printer shown in FIG. 1;

FIG. 4 is a plan view showing the neighborhood of the back tension roller of the printer shown in FIG. 1;

FIG. 5 is an enlarged plan view showing the neighborhood of the back tension roller of the printer shown in FIG. 1;

FIG. 6 is a schematic sectional view showing the neighborhood of the back tension roller shown in FIG. 5;

FIG. 7 is a plan view showing a pre-centering mechanism of the printer shown in FIG. 1;

FIG. 8 is a sectional view of the pre-centering mechanism shown in FIG. 7;

FIG. 9 is a schematic sectional view for explaining the disposition of an image forming part, a driver roller, and a stuff roller of the printer shown in FIG. 1;

FIG. 10 is a block diagram showing a control system of the printer shown in FIG. 1;

FIG. 11 is a timing chart used for a transport control method performed by the control system shown in FIG. 10;

FIG. 12 is a flowchart of printing start processing performed by the control system shown in FIG. 10;

FIG. 13 is a flowchart of printing end processing performed by the control system shown in FIG. 10;

FIG. 14 is a plan view for explaining the operation of correcting a skew of continuous paper by the drive roller;

FIG. 15 is an enlarged plan view showing the neighborhood of the drive roller shown in FIG. 14;

FIG. 16 is a plan view for explaining moment force generated in continuous paper;

FIG. 17 is a plan view showing the state in which continuous paper having slack at the left side thereof is transported downstream of the drive roller;

FIG. 18 is a sectional view of a printer of a second embodiment of the present invention;

FIG. 19 is a schematic plan view of a pre-centering mechanism of the printer shown in FIG. 18;

FIG. 20 is a timing chart showing the relationship between detection results of a detection unit and a drive signal to a solenoid;

FIG. 21 is a plan view for explaining the behavior of continuous paper as results of control by a control part;

FIG. 22 is a plan view showing the neighborhood of a detection unit for explaining a skew correction method;

FIG. 23 is a graph showing the relationship between paper edge fluctuation amounts and paper transport speeds in the neighborhood of the detection unit shown in FIG. 22; and

FIG. 24 is a graph for explaining the effects of reducing the amount of continuous paper fluctuation in transfer positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a printer 1 of a first embodiment of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the printer 1 includes: a hopper 10 that stores continuous paper P; a stacker 20 that stores continuous paper P on which designated images are formed; a transporting mechanism 100; an image forming part 200; and a control system 300 (not shown in FIG. 1). FIG. 1 is a sectional view of the printer 1.

The continuous paper p, which has no holes for tractor pins, excels perforated continuous paper in processing and environment aspects, and is inexpensive. It does not matter whether the continuous paper P is paper folded along perforations formed every a given length or a continuous roll of paper. The hopper 10 and the stacker 20 are not described in detail here because they can employ any constructions known to the industry regardless of their names.

The transporting mechanism 100 transports the continuous paper P from the hopper 10 to the stacker 20 and removes and prevents the slack and a horizontal deviation of the continuous paper P so as to form high-quality images on it. The continuous paper P is fed from the hopper 10 to the stacker 20 automatically or manually by the user during initialization of the printer.

The transporting mechanism 100 includes a transporting system 110, a back tension roller part 140, and a pre-centering mechanism 160.

The transporting system 110 transports the continuous paper P. The continuous paper P is transported in a direction F shown in FIG. 1 during printing, and a direction B opposite to the direction F during back feed described later. The present patent application refers to the direction F as a forward direction and the direction B as a backward direction. The transporting system 110 includes round bar guides 112 and 114, a wraparound roller 116, a drive roller 118, a spring 119, plural pinch rollers 120, plural scuff rollers 122, a spring 123, and a scuff driven roller 124. The pinch rollers 120, though omitted in FIG. 1, are shown in FIGS. 2 and 3. The spring 123 and the scuff driven roller 124 are schematically shown in FIG. 9 described later.

The round bar guides 112 and 114, provided between the hopper 10 and the back tension roller part 140 (and the pre-centering mechanism 160), guide the continuous paper P fed from the hopper 10 to the back tension roller part 140 (and the pre-centering mechanism 160) while bending it in its transport direction. The round bar guides 112 and 114 are plastic or metallic rods that are of identical cylindrical shape and dimensions, and their longitudinal direction is orthogonal to the transport direction of the continuous paper P. The number of round bar guides is not limited to two.

The wraparound roller 116 changes the transport direction F of the continuous paper P to guide the continuous paper P at a designated wraparound angle between the drive roller 118 and the pinch roller 120. The wraparound roller 116 has a slip-proof construction such as metallic or plastic shafts covered with resin so as to produce a desired frictional force between the wraparound roller 116 and the continuous paper P.

The drive roller 118 and the pinch rollers 120 are provided downstream of the pre-centering mechanism 160 with respect to the transport direction F. The drive roller 118 is a driving roller and the pinch rollers 120 are driven rollers. Although the drive roller 118 is upward in this embodiment, the pinch rollers 120 may be upward. FIG. 2 is a schematic sectional view showing the relationship between the drive roller 118 and the pinch rollers 120. FIG. 3 is a schematic plan diagram showing a portion from the back tension roller part 140 to the drive roller 118.

The drive roller 118 is of cylindrical shape wider than the continuous paper P and its rotation shaft 118a is orthogonal to the transport direction. The rotation shaft 118a of the drive roller 118 is directly or indirectly connected to the motor shaft of a motor not shown, and power to the motor is controlled by the control system 300 shown in FIG. 10 described later. Seven of the pinch rollers 120 as shown by the dotted line in FIG. 3 are provided in this embodiment, and juxtaposed at equal intervals in a direction orthogonal to the transport direction F. The width of each pinch roller 120 is narrower than that of the drive roller 118 as shown in FIG. 3, and the distance between the two pinch rollers 120 at both ends is almost equal to the width of the continuous paper P.

Each pinch roller 120 is energized against the drive roller 118 via the continuous paper P by one or more press springs 119. The energized force is far greater than the energized force of the back tension roller part 140 described later. Although energized force by the spring 119 is constant in this embodiment, energized force may be made changeable. In this case, spring pressure by the spring 119 may be made changeable according to the thickness of the continuous paper P, for example.

The energized force of the spring 119 causes a frictional force between the drive roller 118 and the continuous paper P. Using the frictional force, the drive roller 118 guides and transports the continuous paper P to the image forming part 200. The drive roller 118 and the pinch rollers 120 have slip-proof constructions such as metallic shafts covered with resin so as to produce a desired frictional force between the continuous paper P and them.

Three of the scuff rollers 122 are provided in this embodiment, and guide the continuous paper P passing through the image forming part 200 to the stacker 20. The number of the scuff rollers 122 is three as an example in this embodiment. The scuff rollers 122 are driving rollers and transport the continuous paper P by a frictional force between the continuous paper P and them. The relationship among the scuff rollers 122, the press spring 123, and the scuff driven roller 124 is not described in detail here because it is the same as the relationship among the drive roller 118, the spring 119, and the pinch rollers 120. The scuff rollers 122 have the same construction as that of the drive roller 118, except that their diameter is smaller than that of the drive roller 118. Transport force is produced by the nips of the scuff rollers 122 and the scuff driven roller 124. The transport force and transport speed of the scuff rollers 122 will be described later.

The scuff rollers 122 are provided correspondingly to flash fixing units 270 (described later) of the printer 1 of this embodiment. Specifically, if the printer 1 uses fixing units performing fixing processing by pressurization and heating, since heat rollers are used, the scuff rollers 122 may be omitted. A control method of the present invention described later can apply to even printers having no scuff rollers 122.

The back tension roller part 140 removes slack in the continuous paper P when it is fed in the forward direction F or the backward direction B. As shown in FIGS. 4 to 6, the back tension roller part 140 includes a driving (upper) roller 142, a spring 143, and a driven (lower) roller 144, the relationship among which is the same as that among the drive roller 118, the spring 119, and the pinch roller 120. FIG. 4 is a plan view of the back tension roller part 140 and the pre-centering mechanism 160. FIG. 5 is an enlarged plan view of the back tension roller part 140. FIG. 6 is a schematic sectional view of the back tension roller part 140. The length and the number of the rollers 142 and 144, and the interval between them can be freely set so long as the continuous paper P can be transported.

As described later, the back tension roller 142 rotates in the forward direction F at a circumferential speed slower than a paper transport speed when the continuous paper P is transported in the forward direction F, and rotates at a circumferential speed faster than the transport speed of the drive roller 118 when the continuous paper P is transported in the backward direction B (that is, the continuous paper P is fed back). Thereby, the back tension roller 142 can increase tension on the continuous paper P all the time during transport in the transport direction F and the backward direction B. In FIG. 6, D1 designates the forward direction in which paper is transported during printing, and D2 designates the backward direction in which paper is fed back.

The rotation shaft 142a of the roller 142 is directly or indirectly connected to the motor shaft of a motor described later, and power to the motor is controlled by the control system 300 shown in FIG. 10. As shown in FIGS. 4 and 5, the rotation shaft 142a of the roller 142 is orthogonal to the transport direction F. The construction of the roller 142 is the same as that of the drive roller 118, except that its diameter is smaller than that of the drive roller 118.

As shown in FIG. 6, the spring 143 presses the roller 144 against the roller 142 through the continuous paper P. The roller 142 is at a constant distance from the drive roller 118, and does not move vertically as the accumulator described in the above-described patent publication does. The roller 142 can apply a frictional force to the continuous paper P by the press force of the spring 143 and can increase the tension of the continuous paper P by transport force and/or transport speed different from those of the drive roller 118.

The back tension roller part 140 is provided upstream of the pre-centering mechanism 160 with respect to the transport direction. The back tension roller part 140 increases tension on the continuous paper P when the continuous paper P is transported in the forward direction F and the backward direction B. Accordingly, the continuous paper P can be transported without slack between the back tension roller part 140 and the drive roller 118. With conventional constructions, since tension has been applied to continuous paper only between a tension increasing unit and a drive roller, it has been impossible to remove slack occurring in the continuous paper between a paper position regulation part upstream of the tension increasing unit with respect to a transport direction and the tension increasing unit. However, since the back tension roller part 140 of the present embodiment is provided upstream of the pre-centering mechanism 160 with respect to the transport direction F, the continuous paper P can be stably transported without slack.

Since the back tension roller part 140 applies tension to the continuous paper P when the drive roller 118 transports the continuous paper P in the forward direction F and the backward direction B, it has both the functions of conventional accumulators and tension increasing units. Therefore, the transporting apparatus of the present invention can be made more compact in size and lower in cost than the conventional paper transporting apparatus described in the above-described patent publication.

Since the rollers 142 and 144 of the back tension roller part 140 do not move vertically, the transport direction of the continuous paper P is not changed vertically. Accordingly, the back tension roller part 140 excels conventional accumulators in running stability because it causes no skew in the continuous paper P. The back tension roller part 140 also excels conventional tension increasing units including vacuum brakes in that it wears little and can apply constant tension regardless of the width of the continuous paper P.

The pre-centering mechanism 160 has a function for regulating the position of the continuous paper P in a direction orthogonal to the transport direction thereof to prevent a positional deviation in the transfer position TR (in the area where a photosensitive drum 210 and the continuous paper P contact) of an image forming part 200 described later. The pre-centering mechanism 160 has, as shown in FIGS. 1, 3, 7, and 8, a paper guide 161, an edge guide 162, and a skew roller part 170. FIG. 7 is a plan view of the pre-centering mechanism 160, and FIG. 8 is a sectional view of the pre-centering mechanism 160.

The paper guide 161 is formed as a plate member disposed beneath the paper P in parallel to the transport direction, and guides the continuous paper P. The edge guide 162 is, as shown in FIG. 8, a plate-shaped member vertically secured to an edge of the paper guide 161. The edge guide 162 extends along the transport direction, abuts against an edge of the continuous paper P, and regulates the position of the continuous paper P in a direction orthogonal to the transport direction.

The skew roller part 170 includes a pair of upper and lower rollers 170a and 170b, a skew roller base 171, a base rotation shaft 172, connecting members 173a to 173f, a pull spring 174 for pressurizing the upper skew roller 170a, a solenoid 178, and a pull spring 179 for restoring the solenoid 178. FIG. 7 shows connecting members 173b to 173d but omits the skew roller base 171, the connecting member 173a, and the like.

Both the skew rollers 170a and 170b are driven rollers accompanying paper transport. The elastic force of the spring 174 described later causes the upper and lower skew rollers 170a and 170b to nip the continuous paper P and transport it in a direction orthogonal to a roller shaft not shown. The roller shaft is disposed on the skew by a certain angle with respect to the transport direction (or in the direction in which the edge guide 162 extends). Such an angle is set variable as described later. The skew rollers 170a and 170b are mounted on the common skew roller base 171.

The base rotation shaft 172 is, as shown in FIG. 8, secured erectly to the plate-shaped base 171, and disposed beneath the center of the skew rollers 170a and 170b. As a result, the skew roller base 171 can rotate about the rotation shaft 172. The shaft 172 is disposed vertically to the continuous paper P via the point where the skew rollers 170a and 170b nip the continuous paper P. Such a disposition is made to prevent an excess force from being exerted on the continuous paper P when the skew rollers 170a and 170b are driven. FIG. 7 is a top-down view of FIG. 8 and conveniently shows the base rotation shaft 172 positioned at the center of the skew rollers 170a and 170b; actually the base rotation shaft 172 is hidden from view. One end of the base rotation shaft 172 is secured to a lower face 171a of the base 171 and the other end is supported to a rotatable member not shown in the figure.

On the base 171, a pair of plate-shaped connecting members 173a erect in parallel forward and backward of FIG. 8 and are respectively provided with through holes 173g. The plate-shaped connecting members 173a face forward and backward of FIG. 8. On the other hand, the plate-shaped connecting members 173b are machined flat in the T-character shape, and T-character arms are machined in a cylindrical shape and respectively rotatably inserted in the through holes 173g. Alternatively, cylindrical rods are inserted in the through holes 173g so that the plate-shaped connecting members 173b are secured to the cylindrical rods. In any case, the plate-shaped connecting members 173b are rotatably supported to the through holes 173g at the right side edge thereof as shown in FIG. 8. The plate-shaped connecting members 173b face upward and downward of FIG. 8.

The plate-shaped connecting members 173b are connected with the plate-shaped connecting members 173c at the left side edge of FIG. 8. As seen from FIG. 7, the plate-shaped connecting members 173c face the right side and the left side of FIG. 8. The plate-shaped connecting members 173c erect vertically to the plate-shaped connecting members 173b, and are connected with one end of the cylindrical connecting members 173d at the left side thereof as shown in FIG. 8. The upper skew roller 170a is secured to the cylindrical connecting members 173d. One end of the pull spring 174 for pressurizing the upper skew roller 170a is secured to the lower face of the plate-shaped connecting members 173b. The other end of the spring 174 is secured to the upper face 171b of the base 171. As a result, the spring 174 presses the skew roller 170a against the continuous paper P through the connecting members 173b and 173c.

On the other hand, a plate-shaped connecting member 173e is secured vertically and erectly to the upper face 171b of the base 171. The plate-shaped connecting members 173e face the right side and the left side of FIG. 8. The plate-shaped connecting member 173e is connected with one end of cylindrical connecting members 173f at the left side thereof. The lower skew roller 170b is secured to the cylindrical connecting members 173f. As a result, the continuous paper P is nipped by the skew rollers 170a and 170b.

The solenoid 178 is connected to the base 171, as briefly shown in FIG. 7. The solenoid 178 connects with a spring 179 for restoring it. The solenoid 178 is turned on and off to change an angle (referred to as a skew angle) for skewing the continuous paper P. A skew angle corresponds to the angle of a roller shaft (not shown) of the above-described skew roller 170a with respect to the transport direction. The solenoid 178 rotates the skew rollers 170a and 170b about the base rotation shaft 172 to change a skew angle.

In this embodiment, skew angles are changed according to the transport direction of the continuous paper P (that is, the forward direction F or the backward direction B). For example, if the continuous paper P is transported in the forward direction F, a skew angle is changed to +2 degrees, and if transported in the backward direction B, a skew angle is changed to -2 degrees. In this embodiment, for example, if the continuous paper P is transported in the forward direction F, a skew angle is kept constant. However, in another different embodiment, a skew angle is changed even for the duration of time that the continuous paper P is being transported in the forward direction F. Thereby, a resilient force exerted on the continuous paper P from the edge guide 162 can be changed, making it possible to prevent the continuous paper P from being buckled.

Upon going on, the solenoid 178 rotates the base 171 about the rotation shaft 172, and when it goes off, the pull spring 179 restores the solenoid 178, so that the base 171 is also restored. Power to the solenoid 178 is controlled by the control system 300 shown in FIG. 10 described later. Alternatively, the other end of the rotation shaft 172 is connected to a motor shaft not shown, or a gear is formed about the rotation shaft 172 and a gear engaged with that gear is connected to the motor shaft not shown. In any case, the rotation about the rotation shaft 172 of the base 171 can be controlled by the control system 300.

The rollers 170a and 170b are secured to the base 171 through the connecting members 173a to 173f on the skew at a designated angle with respect to the edge guide 162 (and the transport direction F). A skew angle of the rollers 170a and 170b can be changed according to the transport direction of the continuous paper P so that the continuous paper P is energized against the edge guide 162 when the continuous paper P is transported in the forward direction F and the backward direction B. Specifically, since the base 171 can rotate about the rotation shaft 172, the rollers 170a and 170b rotate in response to the rotation of the base 171. As a result, the pre-centering mechanism 160 can, whether the continuous paper P is transported in the forward direction F or the backward direction B, regulate the position of the continuous paper P with respect to a direction orthogonal to the transport direction by pressing it against the edge guide 162.

Although the image forming part 200 forms an image on the continuous paper P by an electrophotographic system, an image forming unit of the present invention is not limited to the electrophotographic system. The image forming part 200 includes the photosensitive drum 210, an optical unit 220, a transfer electrostatic charger 240, and the flash fixing unit 270. These members are briefly shown in FIGS. 1 and 9, and FIG. 11 described later. FIG. 9 is a schematic sectional view for explaining a positional relationship among major components of the image forming part 200, the driver roller 118, and the stuff roller 122. The image forming part 200 includes other components such as an electrostatic charger and a developing unit, which will not be described in detail because any known constructions can apply to the components.

The photosensitive drum 210 has a photosensitive dielectric layer on a rotatable drum-shaped conductive supporting member and is used as an image holding member. For example, the photosensitive drum 210 is a drum-shaped aluminum plate on the surface of which a film about 20 .mu.m thick of separated-function organic photosensitive material is coated, and rotates in the direction of the arrow at a circumferential speed of 70 mm/s. The electrostatic charger is a scorotron electrostatic charger, which supplies a fixed amount of electric charges onto the surface of the photosensitive drum 210. Thereby, the surface of the photosensitive drum 210 can be evenly electrified with about -700V.

The optical unit 220 exposes the photosensitive drum 210 according to image data by use of a light source such as an LED head and a semiconductor laser. As a result of the exposure, the electrification potential of the surface of the photosensitive drum 210 rises to about -70V such that a latent image in accordance with the image data of an image to be recorded is formed. The developing unit supplies fine electrified particles (referred to as toner) supplied from a toner cartridge not shown to the photosensitive drum. By the photosensitive drum 210 and the electrified toner, the latent image on the photosensitive drum 210 is developed and visualized. A developer supplied by the developing unit may be a toner of one ingredient or contain two ingredients such as a toner and a carrier.

The transfer electrostatic charger 240 is configured as a corona electrostatic charger that generates an electric field so as to electrostatically attract the toner and uses a transfer current to transfer the toner image attracted onto the photosensitive drum 210 to the continuous paper P. A transfer guide 242 is provided in the vicinity of the transfer electrostatic charger 240. The transfer guide 242 brings the continuous paper P into intimate contact with the photosensitive drum 210 and separates the continuous paper from the photosensitive drum 210. To form high-quality images on the continuous paper P, it is necessary to prevent horizontal deviation of the paper P in a transfer position TR.

The flash fixing unit 270 irradiates the continuous paper P with light without contact (or applies light energy) and permanently fixes the toner to the continuous paper P. Since the toner after the transfer adheres weakly to the paper P, it will peel off easily. Accordingly, the toner is fixed using energy. However, to obtain sufficient fixing capability, it is necessary to liquefy the solid toner. As energy is applied, the solid toner undergoes changes in state such as semi-solution, spread, and penetration before fixing is completed. As described above, as the flash fixing unit 270, a fixing unit using other than light such as heat and pressure may be used. In this case, a heat roller of the fixing unit contacts the continuous paper P and fixes the toner by pressurizing and heating. In such a fixing unit, since the heat roller has the function of the scuff roller 122 as well, the scuff roller 122 may be omitted. As described above, however, the paper transport control method and the paper transporting apparatus of the present invention can also apply to such a printer.

The control system 300 includes, as shown in FIG. 10, a memory 302, a control part 310, a driver 320 for driving a motor (not shown in the figure) connected to a drive roller 118, a driver 330 for driving a motor (not shown in the figure) connected to a scuff roller 122, a driver 340 for driving a motor (not shown in the figure) connected to a back feed roller 142, a driver 350 for driving a solenoid 178, a communication part 360, different types of sensors 370 such as a photosensor, an operation panel 380, and an oscillator 390 for oscillating clocks. FIG. 10 is a schematic block diagram of the control system 300.

The memory 302 stores data necessary for the control method of the present invention and its execution. The memory 302 includes, ROM, RAM, and the like. For example, the memory 302 stores time TX (X-1, 2 . . . ), velocity VD, and the like.

The control part 310 controls a printing operation by the image forming part 200 while establishing synchronization between the printing operation and a transport operation so that required information is recorded in designated positions of the continuous paper P. The control part 310 executes the control method of the present invention described later through communication with the memory 302. The control part 310 communicates with a host device H (e.g., a personal computer (hereinafter simply referred to as "PC")) (through a printer driver stored in the PC) connected to the printer 1 through the communication part 360. The control part 310 communicates with the operation panel 380 and performs required processing according to input operations of the operation panel 380 by the user of the printer 1.

The oscillator 390 generates basic clocks used for different types of timing processing by use of a pulse oscillator, a counter, and other known technologies. The control part 310, in response to commands from the host device H or the operation panel 380, using the sensor 360 if necessary, controls various drivers 320 to 350 based on the oscillator 390 to control the drive roller 118, the scuff roller 122, and back tension roller 142, and the solenoid 178.

Hereinafter, referring to FIGS. 11 to 13, the control method of the present invention will be described along with the operation of the printer 1. FIG. 11 is a timing chart used for a control method performed by the control system 300. FIG. 12 is a flowchart of printing start processing performed by the control system 300. FIG. 13 is a flowchart of printing end processing performed by the control system 300.

Printing start processing is described with reference to FIGS. 11 and 12. The control part 310 starts printing start processing upon receiving a print command from the host