1. Field of the Invention
The present invention relates to a technique for controlling the tension of a web of printing paper in a printing apparatus for printing on the printing paper while transporting the printing paper along a predetermined transport path.
2. Description of the Background Art
A web printing apparatus for printing on a web (or elongated piece) of printing paper while transporting the printing paper along a predetermined transport path has been conventionally known. The web printing apparatus performs printing in a predetermined printing position on the printing paper while transporting the printing paper by using a plurality of rollers including an infeed roller, an outfeed roller and the like.
Such a web printing apparatus applies a predetermined tension to the printing paper to ensure the flatness of the printing paper in the printing position. Conventional techniques have applied a predetermined tension to the printing paper by setting the rotation speeds of the respective rollers for transporting the printing paper at values increasing gradually in a downstream direction along the transport path. Such techniques, however, have required a user to perform the operation of setting the rotation speeds of the respective rollers. Additionally, the user has been required to set the rotation speeds of the respective rollers again each time the type of printing paper to be used is changed.
Japanese Patent Application Laid-Open No. 2002-248743 discloses a printing apparatus which measures the tension of printing paper to effect feedback control of the rotation speed of an infeed roller so that the result of measurement approaches a predetermined value. Such tension control eliminates the need for the user to set the rotation speeds of the rollers, and also achieves the automatic control of the tension of the printing paper regardless of the type of the printing paper used.
However, when the tension control disclosed in Japanese Patent Application Laid-Open No. 2002-248743 is effected in a plurality of locations in a web printing apparatus, there arises a so-called “hunting” problem.
The present invention is intended for a printing apparatus for printing on a web of printing paper while transporting the printing paper along a predetermined transport path.
According to the present invention, the printing apparatus comprises: a plurality of measuring parts for measuring the tension of the printing paper in a plurality of locations, respectively, along the transport path; a plurality of transport parts for transporting the printing paper near the plurality of measuring parts, respectively; and a controller for controlling the transport speed of the printing paper in the plurality of transport parts, based on tension values measured by the plurality of measuring parts, the controller controlling the transport speed of the printing paper in a first transport part so that a tension value measured by one of the plurality of measuring parts which is located near the first transport part approaches a predetermined value, the first transport part being included among the plurality of transport parts, the controller controlling the transport speed of the printing paper in a second transport part so that tension values measured by two of the plurality of measuring parts which are located immediately upstream and downstream of the second transport part approach each other, the second transport part being included among the plurality of transport parts.
The tension of the printing paper is maintained at the predetermined value in the plurality of locations along the transport path. Because the tension control using the predetermined value as a target value is effected only in a single location, the occurrence of hunting resulting from the interaction between the tensions of the printing paper in the plurality of locations is avoided.
Preferably, the first transport part is located most upstream of all the plurality of transport parts along the transport path.
The transport part in which tension control using the predetermined value as a target value is effected is the transport part located most upstream in the transport path. This eliminates the need to provide another measuring part upstream of the first transport part, thereby reducing the number of measuring parts.
Preferably, the printing apparatus further comprises a plurality of printing parts provided in a plurality of locations, respectively, along the transport path. The plurality of measuring parts measuring the tension of the printing paper being introduced into the plurality of printing parts, respectively.
The tension of the printing paper is maintained at the constant value in the plurality of printing parts. Therefore, the printing position and print quality are consistent in the plurality of printing parts.
Preferably, each of the plurality of printing parts is an inkjet printing part.
The flatness of the printing paper especially required for the inkjet printing part is ensured.
Preferably, the printing apparatus further comprises a delivery part located most downstream in the transport path for transporting the printing paper outwardly at a constant speed.
While maintaining the delivery speed of the printing paper in the delivery part at the constant speed, the printing apparatus can control the transport speed of the printing paper in the plurality of transport parts by using the delivery speed as a reference. Therefore, the tension of the printing paper is suitably controlled.
The present invention is also intended for a method of controlling the tension of a web of printing paper in a printing apparatus, the printing apparatus printing on the printing paper while transporting the printing paper along a predetermined transport path.
It is therefore an object of the present invention to provide a technique capable of maintaining the tension of printing paper at a constant value in a plurality of positions along a transport path in a web printing apparatus.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
A preferred embodiment according to the present invention will now be described with reference to the drawings.
<1. Construction of Printing Apparatus>
A first transport mechanism 21, a first tension sensor 22 and a first printing part 23 are provided in the first transport path part 20. The first transport mechanism 21 is a mechanism for transporting the printing paper P between the feed part 10 and the first tension sensor 22. The first transport mechanism 21 includes an infeed roller 21a and a plurality of nip rollers 21b. The first transport mechanism 21 transports the printing paper P downstream in the transport path of the printing paper P by rotating the infeed roller 21a while holding the printing paper P between the infeed roller 21a and the plurality of nip rollers 21b. The infeed roller 21a is coupled to a first motor 21c, and is rotated by running the first motor 21c.
The first tension sensor 22 is a sensor for measuring the tension of the printing paper P in the first transport path part 20. The first tension sensor 22 is provided between the first transport mechanism 21 and the first printing part 23, and measures the tension of the printing paper P being introduced into the first printing part 23. The first tension sensor 22 may be constructed by using various known pressure sensors. As an example, the first tension sensor 22 may be constructed in such a manner as to convert the pressure received by a roller because of the tension of the printing paper P into an electrical signal through a strain gauge to obtain the electrical signal.
The first printing part 23 is an inkjet printing part for printing on the first surface of the printing paper P. The first printing part 23 includes a plurality of rollers 23a serving as a portion of the transport path of the printing paper P, and a print head 23b for ejecting ink toward the printing paper P. The printing paper P is transported, with the first surface thereof positioned to face upward, while being maintained flat on the plurality of rollers 23a. The print head 23b has a plurality of ink ejection parts (not shown). The print head 23b performs printing on the first surface of the printing paper P by ejecting ink from the ink ejection parts toward the printing paper P being transported on the rollers 23a.
The reversing part 30 is a mechanism for reversing the printing paper P transported from the first transport path part 20 to exchange the first and second surfaces for each other, and then passing the reversed printing paper P to the second transport path part 40. The reversing part 30 includes, for example, a combination of turn bars for changing the angle of transport of the printing paper P.
A second transport mechanism 41, a second tension sensor 42 and a second printing part 43 are provided in the second transport path part 40. The second transport mechanism 41 is a mechanism for transporting the printing paper P between the reversing part 30 and the second tension sensor 42. The second transport mechanism 41 includes an intermediate roller 41a and a plurality of nip rollers 41b. The second transport mechanism 41 transports the printing paper P downstream in the transport path of the printing paper P by rotating the intermediate roller 41a while holding the printing paper P between the intermediate roller 41a and the plurality of nip rollers 41b. The intermediate roller 41a is coupled to a second motor 41c, and is rotated by running the second motor 41c.
The second tension sensor 42 is a sensor for measuring the tension of the printing paper P in the second transport path part 40. The second tension sensor 42 is provided between the second transport mechanism 41 and the second printing part 43, and measures the tension of the printing paper P being introduced into the second printing part 43. The second tension sensor 42 may be constructed by using various known pressure sensors. As an example, the second tension sensor 42 may be constructed in such a manner as to convert the pressure received by a roller because of the tension of the printing paper P into an electrical signal through a strain gauge to obtain the electrical signal.
The second printing part 43 is an inkjet printing part for printing on the second surface of the printing paper P. The second printing part 43 includes a plurality of rollers 43a serving as a portion of the transport path of the printing paper P, and a print head 43b for ejecting ink toward the printing paper P. The printing paper P is transported, with the second surface thereof positioned to face upward, while being maintained flat on the plurality of rollers 43a. The print head 43b has a plurality of ink ejection parts (not shown). The print head 43b performs printing on the second surface of the printing paper P by ejecting ink from the ink ejection parts toward the printing paper P being transported on the rollers 43a.
The delivery part 50 is a mechanism for transporting the printing paper P printed in the second printing part 43 outwardly to the take-up part 60. The delivery part 50 includes an outfeed roller 50a and a plurality of nip rollers 50b. The delivery part 50 transports the printing paper P to the take-up part 60 by rotating the outfeed roller 50a while holding the printing paper P between the outfeed roller 50a and the plurality of nip rollers 50b. The outfeed roller 50a is coupled to a third motor 50c, and is rotated by running the third motor 50c.
The printing apparatus 1 further comprises a controller 70 for controlling the operations of the above-mentioned components. The controller 70 is implemented by a computer having a CPU, a memory, and the like. The controller 70 is electrically connected through a first driver 21d to the first motor 21c. The controller 70 provides a pulse signal to the first driver 21d to run the first motor 21c, thereby rotating the infeed roller 21a. The controller 70 is also electrically connected through a second driver 41d to the second motor 41c. The controller 70 provides a pulse signal to the second driver 41d to run the second motor 41c, thereby rotating the intermediate roller 41a. The controller 70 is also electrically connected through a third driver 50d to the third motor 50c. The controller 70 provides a pulse signal to the third driver 50d to run the third motor 50c, thereby rotating the outfeed roller 50a.
The first tension sensor 22 is electrically connected through a first tension meter 22a to the controller 70. The first tension sensor 22 measures the tension of the printing paper P to transmit the measured tension in the form of an electrical signal to the first tension meter 22a. The first tension meter 22a transmits the electrical signal received from the first tension sensor 22 as a first measured value to the controller 70.
The second tension sensor 42 is electrically connected through a second tension meter 42a to the controller 70. The second tension sensor 42 measures the tension of the printing paper P to transmit the measured tension in the form of an electrical signal to the second tension meter 42a. The second tension meter 42a transmits the electrical signal received from the second tension sensor 42 as a second measured value to the controller 70.
<2. Tension Control of Printing Paper>
Next, the tension control of the printing paper P in the above-mentioned printing apparatus 1 will be described. This printing apparatus 1 controls the tension of the printing paper P by adjusting the rotation speed of the infeed roller 21a and the intermediate roller 41a while rotating the outfeed roller 50a at a predetermined constant speed. The printing paper P is transported outwardly to the take-up part 60 at the constant speed by the outfeed roller 50a. The speeds at which the infeed roller 21a and the intermediate roller 41a transport the printing paper P become slightly different from the speed at which the outfeed roller 50a transports the printing paper P outwardly. This maintains the tension of the printing paper P in the first transport path part 20 and in the second transport path part 40 at a constant value.
In the printing apparatus 1 as described above, the transport speed of the printing paper P in the first transport mechanism 21 is controlled so that the first measured value v1 measured by the first tension sensor 22 approaches the predetermined value pv. The transport speed of the printing paper P in the second transport mechanism 41 is controlled so that the second measured value v2 measured by the second tension sensor 42 approaches the first measured value v1 measured by the first tension sensor 22. Thus, the tension of the printing paper P in the first transport path part 20 and in the second transport path part 40 is maintained at the predetermined value pv. Because the tension control using the predetermined value pv as a target value is effected only in the first transport path part 20, the printing apparatus 1 presents no hunting problem resulting from the interaction between the tension of the printing paper P in the first transport path part 20 and the tension of the printing paper P in the second transport path part 40.
The printing apparatus 1 according to this preferred embodiment is the printing apparatus for printing on the first and second surfaces of the printing paper P. In such a printing apparatus 1, a difference in the tension of the printing paper P is prone to arise across the reversing part 30 unless particular control is exercised. However, effecting the above-mentioned tension control allows the tension of the printing paper P in both locations upstream and downstream of the reversing part 30 to be maintained at the predetermined value pv. Therefore, the same degree of stretch of the printing paper P is attained in the locations upstream and downstream of the reversing part 30, whereby the printing position and print quality are consistent on the first and second surfaces of the printing paper P.
The printing apparatus 1 according to this preferred embodiment is an inkjet printing apparatus. The flatness of the printing paper P in the printing position is especially required for the inkjet printing apparatus. The above-mentioned tension control ensures a high degree of flatness of the printing paper P in the first printing part 23 and in the second printing part 43.
<3. Modifications>
The control of the tension of the printing paper P in the two control positions (the first transport path part 20 and the second transport path part 40) along the transport path is described in the above-mentioned preferred embodiment. The present invention, however, may be adapted to control the tension of the printing paper P in at least three control positions.
In the above-mentioned modification shown in
Although the inkjet printing apparatus is described above, the present invention is not limited to the inkjet printing apparatus, but is applicable to other types of printing apparatuses.
While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
2005-258965 | Sep 2005 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
3561654 | Greiner | Feb 1971 | A |
6092466 | Koch et al. | Jul 2000 | A |
6106177 | Siegl et al. | Aug 2000 | A |
6176410 | Ueda et al. | Jan 2001 | B1 |
6334564 | Kishine et al. | Jan 2002 | B1 |
6499639 | Cote et al. | Dec 2002 | B2 |
6659006 | Brennan et al. | Dec 2003 | B2 |
6782818 | Glockner et al. | Aug 2004 | B2 |
7067039 | Almi et al. | Jun 2006 | B2 |
Number | Date | Country |
---|---|---|
2002-248743 | Sep 2002 | JP |
Number | Date | Country | |
---|---|---|---|
20070051264 A1 | Mar 2007 | US |