US20130099046A1

US20130099046A1 - Printing apparatus and rewinder system

Info

Publication number: US20130099046A1
Application number: US13/645,883
Authority: US
Inventors: Masato Izumi; Kenji Shigeno; Ryosuke Sato
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2011-10-21
Filing date: 2012-10-05
Publication date: 2013-04-25
Also published as: JP2013086442A; JP5858724B2

Abstract

A printing apparatus is provided which can perform skew correction without damaging the print medium when rewinding a print medium into a roll. Therefore, when rewinding of the print medium roll is performed, the two pairs of conveying rollers are employed, and the conveying speed of the conveying roller pair near the print medium roll is set so lower than the conveying speed of the other conveying roller pair located apart from the print medium roll. Further, a guide member for the print medium is provided between the two pairs of the conveying rollers.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a printing apparatus, which includes a roller speed control mechanism for conveying rollers that convey a print medium roll, and to a rewinder system.
2. Description of the Related Art
A loop controller that unwinds a sheet material from a roll, and after forming a loop using the long sheet of the material, proceeds thereafter to rewind the material. This controller relates to a loop control employed for slitter lines for the sheet material, and detects the shape of the loop in order to perform an automatic correction of the roll winding speed to avoid any interference caused by uneven tension or compression being placed on the sheet material.
When a printing apparatus has performed printing on the portion of a print medium wound like a roll, generally, the print medium portion is cut off by a cutter and is discharged, and thereafter, the unprinted print medium portion is rewound into a roll. Further, when the print medium roll is to be unwound for feeding, a loop controller, arranged upstream of the printing unit, and a skew correction mechanism, arranged between the loop controller and the printing unit, are employed to correct skew occurring during the conveying of the print medium portion.
In a case wherein skew occurs in a print medium portion before the portion has passed though the skew correction mechanism, when the print medium portion is formed into a loop, the loop portion would be twisted. And when the rewinding described above is performed for a print medium portion in the skewed state, the amount of skew would be increased between the loop portion and the rewinding portion, due to the loop portion having been twisted.
As another skew correction method, a guide unit is arranged to guide the edge of a print medium to a print medium conveying unit. However, in this case, there is a possibility that when the print medium contacts the guide unit, the print medium will be damaged.

SUMMARY OF THE INVENTION

While taking the above described problems into account, it is one objective of the present invention to provide a printing apparatus that, when rewinding a print medium into a roll, can perform skew correction without damaging the print medium.
To achieve this objective, a printing apparatus according to the present invention includes:
a conveying unit for employing a first roller pair and a second roller pair to feed and convey a print medium that is wound like a roll;
a printing unit for performing printing on the print medium that has been conveyed by the conveying unit;
a rewinding controller for, when the print medium is to be conveyed in a direction opposite the conveyance direction employed for printing and is to be rewound into a roll, providing control for rewinding of the print medium that has been conveyed via the second roller pair and then via the first roller pair;
a guide member arranged between the first roller pair and the second roller pair to perform skew correction for the print medium,

- wherein, to perform rewinding, a print medium conveying speed for the first roller pair is set so lower than a print medium conveying speed for the second roller pair, so that a loop of the print medium is to be formed between the first roller pair and the second roller pair.

According to the printing apparatus of the present invention, since the print medium conveying speed of the first roller pair is lower than the print medium conveying speed of the second roller pair, a loop of print medium is formed between the first roller pair and the second roller pair, and a printing apparatus can be realized whereby, when a print medium roll is to be rewound, skew correction can be performed without the print medium suffering any damage, and a rewinder system can be provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a printing apparatus, for which one embodiment of the present invention can be applied;

FIG. 2 is a block diagram showing the concept of a control unit;

FIG. 3 is a diagram for explaining the operation performed in a single-sided printing mode;

FIG. 4 is a diagram showing the state immediately after a print medium portion was cut off by a cutter;

FIG. 5 is a diagram for explaining the operation performed in a double-sided printing mode;

FIG. 6A is a detailed diagram for explaining a skew correction unit;

FIG. 6B is a detailed diagram for explaining the skew correction unit;

FIG. 7A is a detailed diagram for explaining a print medium supply unit;

FIG. 7B is a detailed diagram for explaining the print medium supply unit;

FIG. 8A is a detailed diagram for explaining the vicinity of a pair of conveying rollers;

FIG. 8B is a detailed diagram for explaining the vicinity of the pair of conveying rollers; and

FIG. 9 is a diagram for explaining a case wherein a plurality of print medium supply units are employed.

DESCRIPTION OF THE EMBODIMENTS

A printing apparatus employing an inkjet printing system will now be described according to one embodiment of the present invention. The printing apparatus for this embodiment is a fast line printer that performs both single-sided printing and double-sided printing by employing a long, continuous print medium (a print medium extended in a conveyance direction a distance that is greater than the length of a print unit area that is repetitively employed for printing (called a page or a unit image)).
Such a printing apparatus is appropriate for printing, for example, a large number of copies for laboratory data. In the specifications for this invention, when a plurality of small images, characters or spaces are present in a single print unit area (one page), the elements included in this unit area are, in their totality, called a unit image.
In other words, the unit image represents a single print unit area (one page) in a case wherein a plurality of pages are sequentially printed on a continuous print medium. The length of the unit area differs depending on the size of an image to be printed. For example, for the photographic print size 3R, the length in a print medium conveyance direction is 135 mm, and for the print size A4, the length in the print medium conveyance direction is 279 mm.
The present invention can be applied for various types of printing apparatuses, such as a printer, a multi-functional printer, a copier and a facsimile machine, or manufacturing apparatuses for these apparatuses. An arbitrary printing system, such as an inkjet system, an electrophotographic system, a thermal transfer system, a dot impact system or a liquid developing system, can be employed. Further, the present invention can be applied not only for a printing processing apparatus, but also a print medium treatment apparatus that performs various treatments (such as printing, processing, coating, irradiating, scanning and inspecting) for a print medium roll.
FIG. 1 is a schematic cross-sectional view for easily understanding the internal arrangement of a printing apparatus for which the present invention can be applied. The printing apparatus of this embodiment employs a print medium roll to perform double-sided printing for a first face of a print medium and a second face that is the reverse side. Inside the printing apparatus, a print medium supply unit 1, a decurling unit 2, a skew correction unit 3, an image printing unit 4, an inspection unit 5, a cutter unit 6, an information printing unit 7, a dryer unit 8, an inverting unit 9, a delivery unit 10, a sorter 11, a discharge unit 12, a humidifier 20 and a control unit 13 are provided as main units.
The print medium is conveyed along a print medium conveyance path, indicated by a solid line in FIG. 1, by a conveying mechanism that includes roller pairs and a belt, and is processed by the individual units. It should be noted that at an arbitrary position on the print medium conveyance path, the side nearest the print medium supply unit 1 is called “upstream”, and the side in the opposite direction is called “downstream”.
The print medium supply unit 1 is a unit that holds and feeds a continuous print medium wound like a roll. The print medium supply unit 1 can store two rolls R1 and R2, and selectively unwind these rolls R1 and R2 to feed the print medium. The number of rolls to be stored is not limited to two, and one roll, or three or more rolls, may be stored.
The decurling unit 2 is a unit that reduces curls (warps) of a print medium that is fed by the print medium supply unit 1. When the print medium passes the decurling unit 2, the decurling unit 2 employs one drive roller and two pinch rollers, and exerts a decurling force to bend the print medium in a predetermined direction, i.e., in a direction opposite the direction in which the print medium is curled. In this manner, curling of the print medium can be reduced. It should be noted that the decurling force of the decurling unit 2 can be adjusted.
The skew correction unit 3 is a unit that corrects the skew of a print medium that passes the decurling unit 2 (the tilt of the print medium relative to the posture supposed to be in the forward direction). The skew correction unit 3 presses, against a guide member, the edge of the print medium that is used as the reference side, and corrects the skew of the print medium.
The image printing unit 4 is a unit that performs printing using a print head 14 and forms an image for the print medium that has been conveyed below. That is, the image printing unit 4 is a processor that performs a predetermined printing process for a print medium. The image printing unit 4 also includes a plurality of conveying rollers. The print head 14 is a line-type print head where ink jet type nozzle arrays are arranged in a range set to cover the maximum width of a print medium that it is assumed is to be employed.
The print head 14 is formed of a plurality of print heads that are arranged in parallel in a conveyance direction. In this embodiment, seven print heads are provided in consonance with seven colors C (cyan), M (magenta), Y (yellow), LC (light cyan), LM (light magenta), G (gray) and K (black). The number of colors and the number of print heads are not limited to seven. The ink jet system may, for example, be a system employing heat-generating elements, a system employing piezoelectric elements, a system employing electrostatic elements, or a system employing MEMS elements.
The individual color inks are supplied respectively from corresponding ink tanks via ink tubes to the print head 14. As will be described later, the print head 14 of the image printing unit 4 can be retracted in a direction away from the print medium. Therefore, the distance between the print head 14 and the print medium can be controlled.
The inspection unit 5 is a unit that employs a scanner and optically reads a check pattern and an image printed on the print medium, and that examines, for example, the nozzle condition of the print head 14, the state wherein the print medium is conveyed and the position of the image to determine whether the image has been correctly printed. The scanner includes a CCD image sensor or a CMOS image sensor.
The cutter unit 6 is a unit that includes a mechanical cutter for cutting off, in a predetermined length, a print medium that has been printed. The cutter unit 6 also includes a plurality of conveying rollers for conveying the print medium to the next stage.
The information printing unit 7 is a unit that reproduces printing associated information (inherent information), such as a serial number or a date stamp, in a non-print area of a sheet cut from the print medium. At this time, characters or codes are reproduced using the ink jet system or the thermal transfer system. A sensor 23 for detecting the leading edge of a print medium cut sheet is also provided upstream of the information printing unit 7 and downstream of the cutter unit 6. That is, the sensor 23 is arranged between the cutter unit 6 and the reproduction location of the information printing unit 7, and detects the edge of the print medium. Based on the detection timing of the sensor 23, the information printing unit 7 controls the timing for information reproduction.
The dryer unit 8 is a unit that heats the print medium that has been printed using the image printing 4, and dries ink applied to the print medium in a short period of time. When the print medium passes the dryer unit 8, hot air is applied to the print medium, at least from below (away from the print face) to dry the ink applied to the face. It should be noted that the drying method is not limited to a single method for applying hot air, but may be a method for performing electromagnetic irradiation, such as the ultraviolet or infrared irradiation, for the surface of the print medium.
The above described print medium conveyance path extending from the print medium supply unit 1 to the dryer unit 8 is called a first path. The first path performs a U-turn between the printing unit 4 and the dryer unit 8, and the cutter unit 6 is positioned at the center of the U-turn.
The inverting unit 9 is a unit that temporarily winds a print medium that has been printed on only one side, and then inverts the sides of the print medium to perform double-sided printing. The inverting unit 9 is located on the route of a path (a loop path) , which extends from the dryer unit 8 via the decurling unit 2 until the image printing unit 4 (this path is called a second path), and along which the print medium that passed the dryer unit 8 is to be conveyed again to the image printing unit 4. The inverting unit 9 includes a rotary winder (drum) that is to be rotated to wind the print medium, and when the continuous print medium that has been printed on one side and has not yet been cut is temporarily wound around the rotary winder.
After winding is completed, the rotary winder is reversely rotated, and the wound print medium is fed to the decurling unit 2 and conveyed to the image printing unit 4. Since the print sides have already been inverted for the print medium conveyed to the image printing unit 4, the image printing unit 4 can perform printing on the reverse side of the print medium. A specific operation for double-sided printing will be described later.
The delivery unit 10 is a unit that conveys the sheets cut from the print medium by the cutter 6 and dried by the dryer unit 8, and delivers the sheets to the sorter 11. The inverting unit 9 is arranged along a path (called a third path) different from the second path along which the inverting unit 9 is located. At the path branching location, a path changing mechanism that includes a movable flapper is arranged in order to guide, into either the second or the third path, the print medium that has been conveyed along the first path.
The sorter 11 and the discharge unit 12 are arranged at the end of the third path beside the printing medium supply unit 1. The sorter 11 is a unit used to sort, into groups, the printed cut sheets of the print medium. The sorted sheets of the print medium are discharged to the discharge unit 12 that includes a plurality of trays. As described above, the third path has a layout that is extended below the print medium supply unit 1 to discharge the print medium to the side opposite the printing unit 4 and the dryer unit 8, with the print medium supply unit 1 inbetween.
As is described above, the components beginning with the print medium supply unit 1 and continuing until the dryer unit 8 are provided in order along the first path. The path forward from the dryer unit 8 branches into the second path and the third path, and the inverting unit 9 is arranged along the second path, which then reaches the first path. The discharge unit 12 is located at the end of the third path.
The humidifier 20 is a unit that generates humid gas (air), and supplies the humid air to a gap between the print head 14 of the image printing unit 4 and the print medium. As a result, the drying of ink in the nozzles of the print head 14 can be avoided. The humidifying type of the humidifier 20 may be an evaporative type, a cool mist type or a steam type. The evaporative type is not only a drum style, as in this embodiment, but also includes a wet membrane style, a drip style and a capillary style.
The cool mist type includes an ultrasonic spray style, a centrifugal atomization style, a high-pressurized spray style and a two-fluid spray style. The steam type includes a steam piping style, an electric heating style, and an electrode style. The humidifier 20 and the image printing unit 4 are connected together by a first duct 21, and the humidifier 20 and the dryer unit 8 are connected by a second duct 22. The dryer unit 8 generates hot, humid air used to dry the print medium. This air is introduced into the humidifier 20 via the second duct 22, and is employed as auxiliary energy for the humidifier 20 to generate moist air. The moist air generated by the humidifier is introduced via the first duct 21 to the image printing unit 4.
The control unit 13 is a unit that controls the individual units of the printing apparatus. The control unit 13 includes a CPU, a storage device, a controller for which there are various types of control portions, an external interface, and an operating unit 15 employed by a user to enter an input/output instruction. The operation of the printing apparatus is performed based on an instruction issued by the controller, or transmitted by a host apparatus 16, such as a host computer, that is connected to the controller via the external interface.
FIG. 2 is a block diagram showing the concept of the control unit 13. The controller (a block enclosed by a broken line) in the control unit 13 includes a CPU (Central Processing Unit) 201, a ROM 202, a RAM 203, an HDD (Hard Disk Drive) 204, an image processor 207, an engine controller 208 and an individual unit controller 209. The CPU 201 totally controls the operations of these units of the printing apparatus. The ROM 202 is employed to store programs executed by the CPU 201 and fixed data required for various operations of the printing apparatus.
The RAM 203 is employed as a work area for the CPU 201 or as a temporary storage area for various received data, or is used to store various setup data. The HDD 204 can store programs executed by the CPU 201, print data, and setup data required for various operations of the printing apparatus, so that the user can read these data from the HDD 204. The operating unit 15 is a user input/output interface, and includes input units, such as hard keys and a touch panel, and output units, such as a display device and a speech generator, for providing information to a user.
A special processor is provided for the units for which fast data processing is required. The image processor 207 performs image processing for print data that is to be handled by the printing apparatus. That is, the image processor 207 converts the color space (e.g., YCbCr) of input image data into the standard RGB color space (e.g., sRGB), or performs various image processes for image data, as needed, such as resolution conversion, image analyzation and image correction. The print data obtained through these image processes is stored in the RAM 203 or the HDD 204.
Based on a control command received, for example, from the CPU 201, the engine controller 208 drives the print head 14 of the image printing unit 4 in accordance with print data. The engine controller 208 also controls the individual conveying mechanisms of the printing apparatus. The individual unit controller 209 is a sub-controller that controls, separately, the print medium supply unit 1, the decurling unit 2, the skew correction unit 3, the inspection unit 5, the cutter unit 6, the information printing unit 7, the dryer unit 8, the inverting unit 9, the delivery unit 10, the sorter 11, the discharge unit 12 and the humidifier 20.
The individual unit controller 209 receives instructions from the CPU 201, and controls the operations of the individual units. The external interface 205 is either a local interface (I/F) or a network /F for connecting the controller to the host apparatus 16. The components described above are interconnected by a system bus 210.
The host apparatus 16 is an apparatus that serves as an image data supply source for permitting the printing apparatus to perform printing. The host apparatus 16 may be a general purpose computer or a dedicated computer, or a special imaging apparatus, such as an image capturing apparatus that includes an image reader, a digital camera or a photo storage device. When the host apparatus 16 is a computer, an OS, application software for generating image data, and a printer driver used for the printing apparatus are installed in the printing apparatus included in the computer. It should be noted that all of these processes are not necessarily provided by using software, and one of, or all of the processes may be provided by hardware.
Next, the basic printing operation will be described. Since the operation differs in the single-sided printing mode and the double-sided printing mode, the operations for the individual printing modes will be described.
FIG. 3 is a diagram for explaining the operation in the single-sided printing mode. FIG. 4 is a diagram showing the state immediately after the print medium was cut by the cutter unit 6. The conveyance path is indicated by thick, solid lines, along which the print medium fed from the print medium supply unit 1 is conveyed to and printed by the image printing unit 4, and the sheets cut from the print medium are delivered to and are discharged by the discharge unit 12.
The print medium is supplied from the print medium supply unit 1, and is processed by the decurling unit 2 and the skew correction unit 3, and printing is performed for the obverse face (first face) of the print medium by the image printing unit 4. Images having a predetermined unit length in a conveyance direction (unit images) are sequentially arranged and printed on the long, continuous print medium. The image bearing print medium is passed through the inspection unit 5, and each unit image is cut from the print medium by the cutter unit 6.
Thereafter, as needed, print associated information is printed on the reverse sides of the cut sheets of the print medium by the information printing unit 7. Then, the sheets cut from the print medium are conveyed, one by one, to the dryer unit 8, and are dried. Following this, the cut sheets are passed through the delivery unit 10, and are discharged to and stacked in the discharge unit 12. Whereas, referring to FIG. 4, after the last unit image is cut off, the print medium that remains on the side of the image printing unit 4 is fed in the reverse direction to the print medium supply unit 1, and is rewound along either the roll R1 or R2. As will be described later, during the rewinding process, the decurling force exerted at the decurling unit 2 is adjusted to low, and the print head 14 is retracted from the print medium.
As described above, in the single-sided printing, the print medium is processed while being conveyed along the first path and the third path, and does not pass along the second path. Summarizing the above description, in the single-sided printing, the control unit 13 controls the execution of sequences (1) to (6) below.

(1) The print medium supply unit 1 feeds a print medium to the image printing unit 4.
(2) The image printing unit 4 repeatedly prints a unit image on the first face of the print medium that is supplied.
(3) The cutter unit 6 repeats cutting of the print medium for each unit image printed on the first face.
(4) The sheets provided by cutting the print medium for each unit image are passed, one by one, through the dryer unit 8.
(5) The individual cut sheets of the print medium passed through the driver unit 8 are conveyed along the third path, and discharged to the discharge unit 12.
(6) After the last unit image is cut off, the print medium that remains on the side of the image printing unit 4 is conveyed in the reverse direction to the print medium supply unit 1.

FIG. 5 is a diagram for explaining the operation in a double-sided printing mode. In the double-sided printing mode, the obverse side (first face) printing sequence is performed, and thereafter, the reverse side (second face) printing sequence is performed. In the obverse side printing sequence performed first, the operations from the print medium supply unit 1 to the inspection unit 5 are the same as those for the single-sided printing. However, in the double-sided printing, the cutting operation is not performed by the cutter unit 6, and the print medium is still in the continuous state when reaching the dryer unit 8. When the surface of the print medium has been dried by the dryer unit 8, the print medium is guided to the path for the inverting unit 9 (the second path), not the path for the delivery unit 10.
The print medium conveyed along the second path is wound around the rotary winder of the inverting unit 9 that is rotated in the forward direction (counterclockwise in FIG. 5). When the image printing unit 4 has completed printing designated for the obverse face, the cutter unit 6 cuts the trailing edge of the print area of the continuous print medium. With the cutting position as a reference, the continuous print medium located downstream in the conveyance direction (the printed portion of the print medium) is conveyed through the dryer unit 8, and is wound by the inverting unit 9 until the trailing edge of the print medium (the cut portion) reaches.
At the same time as winding by the inverting unit 9, the continuous print medium that remains upstream from the cutting position in the conveyance direction (the portion of the print medium close to the image printing unit 4) is returned to the print medium supply unit 1, and is rewound along either the roll R1 or R2, so that the leading edge of the print medium (the cut portion) is not positioned at the decurling unit 2. Since conveying of the print medium in the reverse direction (back-feeding) is performed, this print medium can avoid from running against the print medium portion that is to be fed again in the reverse side printing sequence. As will be described later, during the back-feeding process, the decurling force of the decurling unit 2 is adjusted to low, and the print head 14 is retracted from the print medium.
When the processing for the obverse side printing sequence described above has been completed, the reverse side printing sequence is initiated. The rotary winder of the inverting unit 9 is rotated in the opposite direction to the winding process (clockwise in FIG. 5). The edge of the wound print medium (the trailing edge of the print medium when wound becomes the leading edge when rewound) is fed along a path indicated by a broken line to the decurling unit 2. The decurling unit 2 removes curls provided by the rotary winder.
That is, the decurling unit 2 is located between the print medium supply unit 1 and the image printing unit 4 for the first path, or between the inverting unit 9 and the image printing unit 4 for the second path, and is a unit employed in common for the two paths for performing decurling. The print medium, whose sides have been inverted, is passed through the skew correction unit 3, and is conveyed to the image printing unit 4, which then performs the printing of the reverse side of the print medium.
The image bearing print medium is passed through the inspection unit 5, and is thereafter cut by the cutter unit 6 into print medium sheets for each predetermined unit length that has been set in advance. Since the unit images are printed on both sides of the print media cut sheets, the information printing unit 7 does not perform any printing. The print media cut sheets are then conveyed, one by one, to the dryer unit 8, and are passed on, via the delivery unit 10 and the sorter 11, and are discharged to, and stacked in the discharge unit 12.
As described above, for the double-sided printing, the print medium is processed while being conveyed along the first path, the second path, the first path and the third path in the named order. Summarizing the above description, in the double-sided printing mode, the control unit 13 controls the execution of sequences (1) to (11) below.

(1) The print medium supply unit feeds a print medium into the image printing unit 4.
(2) The image printing unit 4 repeatedly prints a unit image on the first face of the print medium that has been supplied.
(3) The print medium for which the unit images have been printed on the first face is passed through the dryer unit 8.
(4) The print medium passed through the dryer unit 8 is guided to the second path, and is wound around the rotary winder included in the inverting unit 9.
(5) After the repetitive printing on the first face has been completed, the cutter unit 6 cuts the print medium at the end of the last unit image that was printed.
(6) The print medium is wound around the rotary winder until the edge of the cut portion of the print medium has passed the dryer unit 8 and reached the rotary winder, while the print medium remaining on the side of the image printing unit 4 is returned to the print medium supply unit 1.
(7) When the winding has been completed, the rotary winder is rotated in the opposite direction to again supply the print medium along the second path to the image printing unit 4.
(8) The image printing unit 4 repeats the printing of the unit image on the second face of the print medium that has been conveyed along the second path.
(9) The cutter unit 9 repeats the cutting of the print medium for each unit image printed on the second face.
(10) The cut sheets of the print medium provided for each unit image are passed, one by one, through the dryer unit 8.
(11) The individual cut sheets passed through the dryer unit 8 are conveyed along the third path, and are discharged to the discharge unit 12.

FIGS. 6A and 6B are detailed diagrams for explaining the skew correction unit 3. FIG. 6A is a cross-sectional view of the skew correction unit 3, and FIG. 6B is a top view of the skew correction unit 3. A loop of print medium is formed in a loop forming unit 63 by using a conveying roller pair 61 and a conveying roller pair 62. The loop forming unit 63 includes a sensor 64, for detecting the maximum amount of a loop, and a sensor 65, for detecting the minimum amount of a loop, and the convey roller pairs 61 and 62 are employed to control the conveying speed, so that a desired amount of loop is maintained when the print medium is being conveyed.
A skew correction mechanism 66 is located downstream of the loop forming unit 63 to correct the skew of the print medium that is being conveyed. When the skew correction mechanism 66 has corrected the skew, a print medium portion in the loop forming unit 63 is twisted, as indicated by a solid line 67 or a dotted line 68 shown in FIG. 6B.
FIGS. 7A and 7B are detailed diagrams for explaining the print medium supply unit 1. FIG. 7A is a cross-sectional view of the print medium supply unit 1 in the state wherein the print medium is being rewound by applying tension. FIG. 7B is a cross-sectional view of the print medium supply unit 1 in the state wherein the print medium is being rewound by gradually reducing the tension. FIGS. 8A and 8B are detailed diagrams for explaining the vicinity of a conveying roller pair 72.
FIG. 8A is a cross-sectional view and FIG. 8B is a top view. When the print medium, once conveyed, is to be rewound around a print medium member 71 shaped like a roll, the print medium is conveyed by the conveying roller pair 72 and the conveying roller pair 73, and in a case wherein control of such special convey rollers is not performed, tension will continue to be applied along the conveyance path 74. During the rewinding process performed after the printing has been completed, if the print medium is conveyed by applying tension between the loop forming unit 63 and the print medium supply unit 1, a twist to the print medium that has occurred in the loop forming unit 63 will increase skew between the loop forming unit 63 and the print medium supply unit 1.
A guide member 91 for guiding the side edges of the print medium is arranged in the vicinity downstream of the conveying roller pair 72 (see FIGS. 8A and 8B). When the print medium that has been printed is rewound by applying tension under a condition where the degree of skew has been increased, the print medium in the skewed state would strongly contact the guide member 91, and the contact portion of the print medium would be damaged. Further, if the print medium contacts the guide member 91, skew correction for the print medium would not be performed due to strong tension, so that a portion of a print medium that has not been corrected will be rewound as a damaged portion.
Therefore, to prevent an increase in skew, the arrangement in FIG. 7B is employed for this embodiment. Specifically, the conveying speed of the conveying roller pair 72 (first conveying rollers) is lower than the conveying speed of the conveying roller pair 73 (second conveying rollers) to reduce a tension to be applied to the print medium in the conveyance path 74. As a result, a degree of freedom in the movement of the print medium is increased between the conveying roller pair 73 and the conveying roller pair 72, and when the print medium abuts upon the guide member 91, the print medium can move along the guide member 91.
Therefore, when the print medium is rewound, the print medium does not strongly contact the guide member 91, and damage to the print medium does not occur. Of course, during rewinding, skew correction is performed by shifting the print medium that contacts the guide member 91.
As described above, when rewinding of the print medium roll is performed, the two pairs of conveying rollers are employed, and the conveying speed of the conveying roller pair near the print medium roll is set so lower than the conveying speed of the other conveying roller pair located apart from the print medium roll. Further, a guide member for the print medium is provided between the two pairs of the conveying rollers. With this arrangement, a printing apparatus can be provided, wherein when the print medium roll is rewound, skew correction can be performed without damaging the printing medium.

Other Embodiment

The other embodiment of the present invention will now be described. Since the basic arrangement of this embodiment is the same as that for the above described embodiment, only a characteristic arrangement will be described.
In the above described embodiment, only one print medium supply unit 1 has been employed; however, in this embodiment, a plurality of print medium supply units 1 are employed.
FIG. 9 is a diagram for explaining a case wherein a plurality of print medium supply units are arranged. Four print medium supply units 81, 82, 83 and 84, shaped like reels, are provided, and conveying roller pairs 811, 821, 831 and 841 are arranged, respectively, for these units. A conveying roller pair 85 is located downstream of the juncture of conveyance paths 812, 822, 832 and 842.
The conveying speeds of the conveying roller pairs 811, 821, 831 and 841 are changed in accordance with the conveying distances between the conveying roller pair 85 and the conveying roller pairs 811, 821, 831 and 841, so that, during the rewinding process, skew caused by a twist in a print medium in a loop forming unit 63, is to be corrected and damage on the print medium is to be reduced. Specifically, when the conveying distance between the conveying roller pairs is long, the speeds of the conveying roller pairs 811, 821, 831 and 841 are set low.
That is, the amount of the loop being loosened is formed in accordance with the distance, so that in a case wherein the conveying distance is long, the degree to which the loop is loosened is increased for the distances, and in a case wherein the conveying distance is short, the amount the loop is loosened is reduced for the distances. In this manner, the optimal loops are formed for the individual print medium supply units 1 to perform rewinding. With this arrangement, a printing apparatus can be provided wherein, when a print medium roll is to be rewound, the skew correction can be performed without damaging a print medium.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2011-231280, filed Oct. 21, 2011, which is hereby incorporated by reference herein in its entirety.

Claims

What is claimed is:

1. A printing apparatus comprising:

a conveying unit for employing a first roller pair and a second roller pair to unwind a roll of print medium, and to convey the print medium;

a printing unit for performing printing on the print medium that has been conveyed by the conveying unit;

a rewinding controller for, when the print medium is to be conveyed in a direction opposite a conveyance direction employed for printing, and to be rewound onto the roll, rewinding the print medium that has been conveyed via the second roller pair and then via the first roller pair;

a guide member arranged between the first roller pair and the second roller pair to perform skew correction for the print medium,

wherein, for performing rewinding, a print medium conveying speed for the first roller pair is set lower than a print medium conveying speed for the second roller pair, so that a loop of the print medium can be formed between the first roller pair and the second roller pair.

2. The printing apparatus according to claim 1, wherein a plurality of sets for the first roller pairs are provided, and wherein, for the individual sets of the first roller pairs, the print medium conveying speed is set lower as a print medium conveyance path from the second roller pair to the first roller pair is extended.

3. The printing apparatus according to claim 2, wherein the conveying unit feeds the print medium from a plurality of rolls of the print medium, which correspond to the plurality of sets for the first roller pairs, and conveys the print medium by employing a plurality of conveyance paths.

4. The printing apparatus according to claim 3, wherein a guide member for guiding the print medium in a direction perpendicular to the conveyance direction is located between the first roller pairs and the conveyance paths, downstream of the first roller pair, in the conveyance direction.

5. A printing apparatus comprising:

a printing unit for performing printing of the print medium that has been conveyed by the conveying unit;

a rewinding controller for, when the print medium is to be conveyed in a direction opposite a conveyance direction employed for printing, and is to be rewound into a roll, rewinding the print medium that has been conveyed via the second roller pair and then via the first roller pair; and

wherein, to perform rewinding, a print medium conveying speed for the first roller pair is set lower than a print medium conveying speed for the second roller pair, so that tension applied to the print medium is reduced.

6. A rewinder system comprising:

a conveying unit for employing a first roller pair and a second roller pair to unwind a roll of print medium and convey the print medium;

a rewinding controller for, when the print medium is to be conveyed in a direction opposite a conveyance direction and to be rewound into the roll, controlling rewinding of the print medium that has been conveyed via the second roller pair and then via the first roller pair; and

a guide member arranged between the first roller pair and the second roller pair to correct skew of the print medium.