CLIAMS:What is claimed is:
1. A conveyance device comprising:
a roll storage unit that stores a continuous sheet conveyance medium in a roll;
a tractor that sequentially engages engaging parts in engagement holes formed along the length of the conveyance medium and conveys the conveyance medium stored in the roll storage unit;
a roll drive unit that delivers the conveyance medium stored in the roll storage unit toward the tractor;
a slack detection unit that detects slack in the conveyance medium between the roll storage unit and the tractor; and
a control unit that controls the roll drive unit based on the detection value of the slack detection unit.

2. The conveyance device described in claim 1, wherein:
the control unit drives the roll drive unit and delivers the conveyance medium toward the tractor when the slack detection unit does not detect slack in the conveyance medium.

3. The conveyance device described in claim 1, wherein:
the control unit stops the roll drive unit when the slack detection unit detects slack in the conveyance medium.

4. The conveyance device described in claim 1, further comprising:
a paper feed roller that conveys the conveyance medium on the downstream side of the tractor in the conveyance direction.

5. The conveyance device described in claim 1, wherein:
the paper feed roller drives, and the tractor follows, while the conveyance medium is conveyed.

6. The conveyance device described in claim 4, wherein:
the roll drive unit drives independently of the paper feed roller.

7. The conveyance device described in any of claims 1 to 6, wherein:
conveyance of the conveyance medium is intermittent.

8. A printing device that prints on a conveyed medium, comprising:
the conveyance device described in any of claims 1 to 7.

9. A conveyance method of a conveyance device having a roll storage unit that stores a continuous sheet conveyance medium in a roll, a tractor that sequentially engages engaging parts in engagement holes formed along the length of the conveyance medium and conveys the conveyance medium stored in the roll storage unit, a roll drive unit that delivers the conveyance medium stored in the roll storage unit toward the tractor, and a slack detection unit that detects slack in the conveyance medium between the roll storage unit and the tractor, comprising:
controlling the roll drive unit based on the detection value of the slack detection unit.

10. The conveyance method described in claim 9, wherein the control unit:
repeatedly drives the roll drive unit and delivers the conveyance medium toward the tractor when the slack detection unit does not detect slack in the conveyance medium; and
stops the roll drive unit when the slack detection unit detects slack in the conveyance medium.
,TagSPECI:SPECIFICATION
Conveyance device, printer, and conveyance method

BACKGROUND
1. Technical Field
[0001]
The present disclosure relates to a device for conveying continuous sheet media stored in a roll, for example, and relates more particularly to a conveyance device that can precisely convey a medium without damaging the medium even when the conveyed medium is stored in a large roll and is conveyed intermittently at high speed.
2. Related Art
[0002]
A device for conveying sheet media is typically used in printers and other devices for processing paper or other sheet media. Such conveyance devices commonly convey continuous sheet media stored in a roll, for example, by means of roller pairs that hold the medium from above and below.
[0003]
The ability to convey the processed medium precisely is desirable in such conveyance devices, and particularly in conveyance devices used in printers, in order to enable high quality processing (such as printing) of the conveyed medium (such as paper), and many different designs have been proposed.
[0004]
For example, maintaining a constant load on the upstream side, known as back tension (the tension from the upstream side), of the paper feed rollers (delivery rollers) that feed the conveyed medium to the processing position has been proposed. When the conveyed medium is stored in a roll, such as when roll paper is used, for example, one method uses a tension lever to buffer the heavy load from the conveyed medium stored in a roll.
[0005]
As another example, configurations that reduce this back tension to zero have also been proposed. More specifically, this configuration constantly produces slack in the conveyed medium on the upstream side of the paper feed rollers (delivery rollers).
[0006]
JP-A-2012-45876 also teaches a conveyance control method that drives both a paper feed roller and a tractor when printing on continuous paper, and can precisely convey the continuous paper without applying a heavy a load.
[0008]
However, when the conveyed medium is roll paper with a large diameter, and must be conveyed intermittently at high speed using the foregoing configuration that maintains a constant back tension, the paper feed rollers (delivery rollers) start and stop frequently, and control that maintains constant back tension is difficult.
[0009]
Furthermore, in order to control the position of the conveyed medium (paper) with no tension using the configuration that maintains zero back tension, guides must be provided on the left and right sides of the medium, and creases in the edges of the conveyed medium and skewing can easily occur.
[0010]
When the load from the storage position of the conveyed medium is high, such as when the conveyed medium is a large diameter roll, the conveyed medium can also be damaged where the tractor pins engage the conveyed medium, and the method taught in JP-A-2012-45876 does not address this problem.

SUMMARY
[0011]
A conveyance mechanism for continuous sheet media stored in a roll according to the present disclosure enables conveying the medium with high precision without damaging the medium even when the conveyed medium is stored in a large diameter roll and is conveyed intermittently at high speed.
[0012]
To achieve the foregoing object, a conveyance device according to the disclosure is characterized by the conveyance device having a roll storage unit that stores a continuous sheet conveyance medium in a roll; a tractor that sequentially engages engaging parts in engagement holes formed along the length of the conveyance medium and conveys the conveyance medium stored in the roll storage unit; a roll drive unit that delivers the conveyance medium stored in the roll storage unit toward the tractor; a slack detection unit that detects slack in the conveyance medium between the roll storage unit and the tractor; and a control unit that controls the roll drive unit based on the detection value of the slack detection unit.
[0013]
Preferably, the control unit drives the roll drive unit and delivers the conveyance medium toward the tractor when the slack detection unit does not detect slack in the conveyance medium, and stops the roll drive unit when the slack detection unit detects slack in the conveyance medium.
[0014]
Further preferably, the conveyance device also has a paper feed roller that conveys the conveyance medium on the downstream side of the tractor in the conveyance direction.
[0015]
Further preferably, the paper feed roller drives, and the tractor follows, while the conveyance medium is being conveyed.
[0016]
Further preferably, the roll drive unit drives independently of the paper feed roller.
[0017]
Further preferably, the conveyance medium is conveyed intermittently.
[0018]
Another aspect of the disclosure is a printing device that has the conveyance device described above, and executes a printing process on the conveyance medium.
[0019]
Another aspect of the disclosure is a conveyance method of a conveyance device having a roll storage unit that stores a continuous sheet conveyance medium in a roll, a tractor that sequentially engages engaging parts in engagement holes formed along the length of the conveyance medium and conveys the conveyance medium stored in the roll storage unit, a roll drive unit that delivers the conveyance medium stored in the roll storage unit toward the tractor, and a slack detection unit that detects slack in the conveyance medium between the roll storage unit and the tractor, the control method controlling the roll drive unit based on the detection value of the slack detection unit.
Preferably, the control method repeatedly drives the roll drive unit and delivers the conveyance medium toward the tractor when the slack detection unit does not detect slack in the conveyance medium; and stops the roll drive unit when the slack detection unit detects slack in the conveyance medium.
Other objects and attainments together with a fuller understanding of the disclosure will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the configuration of a printer with a conveyance mechanism according to the disclosure.
FIG. 2 is a bird's-eye view of part of the printer 2.
FIG. 3 describes slack detection by the slack sensor 29.
FIG. 4 is a flow chart describing control of the roll drive unit 28.

DESCRIPTION OF EMBODIMENTS
[0021]
A preferred embodiment of the present disclosure is described below with reference to the accompanying figures. The technical scope of the present disclosure is, however, not limited to this embodiment. Note, further, that like and similar parts are identified by the same reference numerals in the accompanying figures.
[0022]
FIG. 1 illustrates the configuration of a printer with the conveyance mechanism according to the disclosure. The printer 2 shown in FIG. 1 is a printing device according to this embodiment of the disclosure, and this printing device conveys paper 26 as an example of a print medium stored as a paper roll 25 to the print position by means of a tractor 30 and paper feed roller 32 and prints. By controlling driving the roll drive unit 28 based on detected output from the slack sensor 29 during conveyance, the printer creates slack in the paper 26 on the upstream side of the tractor 30 and conveys the medium with high precision without damaging the conveyed medium.
[0023]
As shown in FIG. 1, the printer 2 is a device that receives instructions from a computer or other host device 1 and executes a printing process, and in this example is a serial inkjet printer. The paper 26, which is continuous paper, is stored in a large diameter paper roll 25 in the roll storage unit 27, and has multiple sprocket holes formed at an equal interval along both sides of the paper width. The paper 26 is conveyed intermittently at a relatively high speed during the printing process.
[0024]
FIG. 1 schematically illustrates the configuration of the printer 2, and this printer 2 has a print system that controls the print content and applies a printing process to the paper 26, and a conveyance system that conveys the paper 26.
[0025]
The print system includes the print control unit 21, and the print control unit 21 receives print instructions from the host device 1 and outputs print commands to the head unit 23, and outputs paper 26 conveyance commands to the conveyance control unit 22 of the conveyance system, according to the print instructions. The head unit 23 prints on the paper 26 positioned between the head unit 23 and platen 24 according to the print commands.
[0026]
As shown in FIG. 1, the conveyance operation of the conveyance system is executed until the paper 26, which is the print medium, is conveyed from the roll storage unit 27 through the conveyance path 34 to the head unit 23, and is then discharged through the discharge roller 35 from the printer 2.
[0027]
In order to convey paper to the head unit 23, a paper feed roller 32 including a pair of rollers is disposed to the conveyance path 34 on the upstream side of the head unit 23 as shown in FIG. 1. This pair of rollers is disposed at mutually opposing top and bottom positions with the paper 26 therebetween, the bottom roller being the drive roller and the top roller being the driven roller.
[0028]
The drive roller is turned by the torque of a motor transferred through a speed reducing mechanism, and moves the paper 26 by means of the friction with the paper 26 held between the drive roller and the driven roller. When conveying the paper 26, the driven roller is held with pressure applied to the paper 26, and rotates in conjunction with rotation of the drive roller. Note that the roller is preferably finished with surface processing that reduces deformation and increases friction.
[0029]
The speed reducer and motor that turn the drive roller are the roller drive unit 33 shown in FIG. 1, and drive the drive roller as controlled by the conveyance control unit 22. A rotary encoder not shown is also disposed to the drive roller or the driven roller, and the conveyance control unit 22 controls the paper feed roller 32 based on the output signal from this rotary encoder.
[0030]
The paper feed roller 32 handles conveying, that is, intermittently feeding as described above, the paper 26 during the printing process.
[0031]
The tractor 30 is located on the upstream side of the paper feed roller 32, and includes teeth 301 (pins, engaging parts) that are inserted to and engage the sprocket holes in the paper 26, a tractor belt on the outside surface of which the teeth 301 are formed at a regular interval, and a drive sprocket and driven sprocket on which the tractor belt is mounted. The speed reducer and motor that turn the drive sprocket are the tractor drive unit 31 shown in FIG. 1, and drive the drive sprocket as controlled by the conveyance control unit 22.
[0032]
The tractor 30 is driven when conveying the leading end of the paper 26 to the position of the paper feed roller 32 when the paper roll 25 is set in the roll storage unit 27, for example. The tractor 30 also simply follows during intermittent conveyance in the printing process. When driven, the drive sprocket turns and rotates the tractor belt by the drive force of the motor in the tractor drive unit 31, sequentially engages the teeth 301 in the sprocket holes, and conveys the paper 26.
[0033]
The paper roll 25 stored in the roll storage unit 27 can be turned on the center spindle by the roll drive unit 28. The roll storage unit 27 has a shaft member that passes through the spindle supporting the paper roll 25, and a pair of flanges disposed on opposite sides of the width of the paper roll 25. The roll drive unit 28 includes a motor that turns the shaft member of the roll storage unit 27, and a speed reducer that transfers drive power from the motor to the shaft member, and rotationally drives the shaft member as controlled by the conveyance control unit 22.
[0034]
When the shaft member is turned by the roll drive unit 28, the paper roll 25 rotates on its spindle, and the paper 26 is conveyed to the tractor 30 side (downstream side). The paper roll 25 is rotationally driven by the roll drive unit 28 when the paper 26 is conveyed, and drive control is described more specifically below.
[0035]
FIG. 2 us a bird's-eye view of part of the printer 2. Shown in FIG. 2 are the head unit 23 and platen 24 of the above printing system, and the roll storage unit 27, tractor 30, and paper feed roller 32 of the above conveyance system. As shown in FIG. 2, the tractor 30, paper feed roller 32, and head unit 23 are sequentially disposed in order to the downstream side from the position where the paper roll 25 is held, and the paper 26 delivered from the paper roll 25 is conveyed through the tractor 30 from the paper feed roller 32 to the position of the head unit 23.
[0036]
A slack sensor 29 (slack detection unit) is also disposed where the paper roll 25 is stored (held). The slack sensor 29 is a sensor that detects slack in the paper 26 between the position where it is stored as paper roll 25 and the position of the tractor 30, and more specifically detects whether or not there is sufficient slack and outputs to the conveyance control unit 22. In this embodiment, the slack sensor 29 determines there is sufficient slack if the bottom end of the paper 26 stored (held) in the roll storage unit 27 is below a specific position, and determines there is not sufficient slack if this bottom end is above this specific position.
[0037]
FIG. 3 is used to describe slack detection by the slack sensor 29. The condition of the paper 26 and the paper roll 25 stored (held) in the roll storage unit 27 is illustrated in FIG. 3 wherein the arrows in the figures indicate the direction in which the paper 26 is delivered and conveyed. FIG. 3 (A) shows an example in which the remaining amount of paper 26 stored on the paper roll 25 is relatively great, and the slack is sufficient.
[0038]
The slack sensor 29 detects if the paper 26 is present at a specific vertical position, and outputs an appropriate signal (ON signal) to the conveyance control unit 22 if the paper 26 is present. In the example shown in FIG. 3 (A), the bottom end of the paper 26 is below the position where the slack sensor 29 is disposed, and an ON signal indicating the paper 26 is present, that is, a signal indicating there is sufficient slack, is output. The vertical position of the slack sensor 29 is a distance h below the center axis of the stored paper roll 25, and this position is the above specific position for determining the position of the bottom of the paper 26.
[0039]
Note that the slack sensor 29 could be a transmissive or reflective photosensor, a contact sensor, or other type of mechanical sensor known from the literature.
[0040]
FIG. 3 (B) shows an example in which the remaining amount of paper 26 stored in the paper roll 25 is relatively great, and the slack is not sufficient. In this event, the slack sensor 29 outputs to the conveyance control unit 22 a signal (OFF signal) indicating that the paper 26 is not present at the specific position, that is, a signal indicating there is not enough slack.
[0041]
FIG. 3 (C) shows an example in which the remaining amount of paper 26 stored in the paper roll 25 is relatively small, and the slack is sufficient. In this event, the slack sensor 29 outputs an ON signal, that is, a signal indicating there is sufficient slack, as in the example shown in FIG. 3 (A).
[0042]
As will be understood by comparing the examples in FIG. 3 (A) and (B) and the example shown in FIG. 3 (C), the amount of slack that is determined to be sufficient increases as the amount of remaining paper 26 decreases, and distance h is set so that the amount of slack that is determined sufficient is appropriate even when a new paper roll 25 of the largest diameter is loaded. More specifically, when the ON signal is output based on the above decision, the amount of slack is sufficient regardless of how much paper 26 is left.
[0043]
Referring again to FIG. 1, a cutter 36 is disposed at the downstream end of the conveyance path, and operates to cut the paper 26 when the printing process is finished.
[0044]
The conveyance control unit 22 shown in FIG. 1 is the part that controls the conveyance system, and controls the paper 26 conveyance operation based on instructions from the print control unit 21. This control by the conveyance control unit 22 drives the foregoing paper feed roller 32, tractor 30, and roll drive unit 28 at specific times and conveys the paper 26. The printer 2 according to this embodiment is characterized by controlling the roll drive unit 28 based on the detection signal from the slack sensor 29 as described more specifically below.
[0045]
While not shown in the figures, the conveyance control unit 22 has a CPU, ROM, RAM, and NVRAM (nonvolatile memory), and the process run by the conveyance control unit 22 is executed primarily by the CPU operating according to a program stored in ROM.
[0046]
Note, further, that the conveyance system including the roll storage unit 27, roll drive unit 28, tractor 30, paper feed roller 32, and conveyance control unit 22 corresponds to the conveyance device according to the disclosure.
[0047]
The printer 2 configured as described above is characterized by conveyance control of the paper 26, and particularly controlling rotation of the paper roll 25 by the roll drive unit 28, as described with reference to a specific example below.
[0048]
FIG. 4 is a flow chart showing steps in the control of the roll drive unit 28. To start conveying the paper 26, the conveyance control unit 22 first instructs the roll drive unit 28 to start driving (step S1 in FIG. 4). The roll drive unit 28 then drives in response to the command, and the paper roll 25 turns in the direction in which the paper 26 is delivered downstream.
[0049]
Thereafter, each time the signal output at a specific timing (at a specific time interval) from the slack sensor 29 is received, the conveyance control unit 22 determines based on the signal whether or not there is sufficient slack (step S2 in FIG. 4). In other words, the conveyance control unit 22 checks whether or not there is sufficient slack between the stored paper roll 25 and the tractor 30.
[0050]
The conveyance control unit 22 continues driving the roll drive unit 28 until it is determined there is sufficient slack (until the above ON signal is received) (step S2 in FIG. 4 returns NO), and when sufficient slack is detected (step S2 in FIG. 4 returns YES), informs the part that controls other devices in the conveyance system that conveyance is possible (step S3 in FIG. 4). As a result of this report, driving the tractor 30 starts if media conveyance is immediately after paper roll 25 was loaded, and conveyance by the paper feed roller 32 starts if the leading end of the paper 26 has already been conveyed to a position downstream from the paper feed roller 32.
[0051]
The conveyance control unit 22 outputs a stop command to the roll drive unit 28 after sending this report (step S4 in FIG. 4), driving the roll drive unit 28 therefore stops, and rotation of the paper roll 25 stops accordingly.
[0052]
If the conveyance process has not ended (step S5 in FIG. 4 returns NO), the conveyance control unit 22 checks the slack as in step S2 (step S6 in FIG. 4). The conveyance control unit 22 keeps the roll drive unit 28 stopped (step S6 in FIG. 4 returns YES) until it determines there is not sufficient slack (until the above OFF signal is received), and when insufficient slack is detected (step S6 in FIG. 4 returns NO), instructs the roll drive unit 28 to start driving (step S7 in FIG. 4). The roll drive unit 28 then drives according to the instruction and the paper roll 25 turns in the direction delivering the paper 26 downstream. More specifically, the paper roll 25 turns in the direction increasing slack.
[0053]
If the conveyance process has not ended (step S8 in FIG. 4 returns NO), the conveyance control unit 22 checks the slack as in steps S2 and S6 (step S9 in FIG. 4). The conveyance control unit 22 continues driving the roll drive unit 28 until it determines there is sufficient slack (step S9 in FIG. 4 returns NO), and when sufficient slack is detected (step S9 in FIG. 4 returns YES), goes to step S4. More specifically, the conveyance control unit 22 outputs a stop command to the roll drive unit 28, the roll drive unit 28 stops driving, and rotation of the paper roll 25 stops accordingly.
[0054]
These steps then repeat until the conveyance process is completed. When the conveyance process is completed (step S5 or S8 in FIG. 4 returns YES), the conveyance control unit 22 ends control of the roll drive unit 28 this time.
[0055]
Control by the conveyance control unit 22 as described above causes the roll drive unit 28 to be driven and the paper roll 25 to turn in the direction increasing slack when the paper 26 is being conveyed and there is not sufficient slack between the paper roll 25 and the tractor 30. By appropriately setting the amount of slack considered sufficient, slack can always be maintained in the paper 26 between the paper roll 25 and the tractor 30 while the paper 26 is being conveyed.
[0056]
As described above, when conveying paper 26 with the printer 2 and conveyance system according to this embodiment, the roll drive unit 28 is controlled so that there is always slack in the paper 26 between the paper roll 25 and the tractor 30, and the load from the paper roll 25 is therefore not applied to the tractor 30, that is, there is zero back tension on the tractor 30. The paper 26 will therefore not be damaged where the tractor 30 and paper 26 engage due to back tension.
[0057]
Furthermore, because the tractor 30 maintains constant back tension on the paper feed roller 32 due to the configuration of the paper feed roller 32 and tractor 30, the conveyance system according to this embodiment can maintain stable, precise paper feed control. In addition, the side to side position and direction of the paper 26 can be controlled and skewing and meandering can be minimized by the teeth 301 of the tractor 30 engaging the sprocket holes of the paper 26. The pressure of the paper feed roller can also be increased because the position of the paper 26 is firmly controlled by the tractor 30, media conveyance is therefore resistant to variations in load and other external factors, and stable conveyance is possible.
[0058]
By maintaining sufficiently great slack in the paper 26 between the paper roll 25 and tractor 30 relative to the high speed, intermittent conveyance operation of the paper feed roller 32, and driving the roll drive unit 28 independently of other conveyance devices, starting and stopping rotationally driving the paper roll 25 can be controlled smoothly.
[0059]
The printer 2 according to this embodiment can also print with high quality even during high speed serial printing using a large diameter paper roll because high precision conveyance of the paper is possible and there is no danger of damaging the paper.
[0060]
The foregoing embodiment is described using paper as the print medium, but the disclosure is not so limited and can be used with any type of sheet medium.
[0061]
The foregoing embodiment describes printing as the process applied to the conveyed sheet medium using a printer having the conveyance system of the disclosure, but the disclosure can be applied to various devices that process sheet media.
[0062]
Although the present disclosure has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present disclosure as defined by the appended claims, unless they depart therefrom.