Reference is made to commonly-assigned copending U.S. patent application Ser. No. 12/627,018 filed Nov. 30, 2009 entitled “MEDIA TRANSPORT SYSTEM FOR NON-CONTACT PRINTING”, by Muir et al. and to commonly-assigned copending U.S. patent application Ser. No. 12/627,003 (issued as U.S. Pat. No. 8,308,037) filed Nov. 30, 2009 entitled “PRINT MEDIA TENSIONING APPARATUS”
This invention relates generally to the field of digitally controlled printing systems, and in particular to the media transport portion of these systems.
In high speed inkjet printing systems, print media typically moves through the printing system as a continuous web of print media rather than individual sheets of print media. As the web of media passes through the print system, the print media is held under tension. Variations in the tension of the print media across the width of the print media cause the print media to drift laterally. Precision alignment of the rollers which support and guide the print media reduces the tendency of the print media to drift laterally, but achieving precision alignment of the rollers is, typically, a costly process. As precision alignment of the rollers can reduce or even eliminate drifting of the print media, conventional printing systems typically include servo-controlled web guides to steer the print media to the desired lateral position. While such web guides can be effective, they add significant cost to the printing system.
As such, there is an ongoing need to provide, at a relatively low cost, an apparatus that equalizes the tension of the print media across the width of the print media to reduce or even eliminate the tendency of the print media to drift laterally.
According to an aspect of the present invention, an apparatus for maintaining uniform tension across a width of a web is provided. The apparatus includes a frame, a roller, a first coupling, a second coupling, and a third coupling. The roller includes a shaft about which the roller rotates. The roller shaft defines an axis of rotation and includes a first end and a second end. The first coupling includes a first arm and a first joint that couples the first end of the roller shaft to the frame such that the roller shaft is free to rotate. The first joint is offset relative to the roller axis by a first distance. The second coupling includes a second arm, a second joint, and a third joint that couples the second end of the roller shaft to the frame. The second arm is free to pivot relative to the roller shaft and the frame through the second joint and the third joint. The third joint is offset relative to the roller axis by a second distance that is substantially equal to the first distance and in the same direction relative to the roller axis. The third coupling includes a third arm and a fourth joint that couples the second end of the roller shaft to the frame. The third arm is coupled to the frame through the fourth joint. The fourth joint is offset relative to the roller axis by a third distance that is substantially equal to the first distance. The offset is in an opposite direction relative to the roller axis.
According to another aspect of the present invention, the fourth joint is constrained to lie substantially in a plane defined by the first joint, the third joint, and a center point located along the length of the roller shaft. The third coupling further comprises a fourth arm and a fifth joint that couples the second end of the roller shaft to the frame, the third arm being coupled to a first end of the fourth arm through the fourth joint located between the third arm and the fourth arm such that the fourth arm is free to pivot relative to the third arm, the fourth joint being offset relative to the roller axis by a second distance that is substantially equal to the first distance but in an opposite direction relative to the roller axis, the second end of the fourth arm being coupled to the frame through the fifth joint such that the fourth arm is free to pivot relative to the frame.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
Although the term “paper” is used in this application to refer to print media that is printed on by a printing system, the term “print media” should not be restricted to paper or paper based media. Instead, print media includes any media type that is printed on by the printing system, for example, those that include polymeric or metallic films or foils. Additionally, print media includes media types that include those having woven or non-woven structures.
In
Print media transport systems, particularly systems that utilize exact constraint or kinematic design, can use various arrangements of castered and gimbaled rollers in order to maintain uniform web tension and reduce or eliminate unnecessary constraints that would otherwise cause unwanted steering or other misalignment along the media path. For example, one such system that applies kinematic principles along the media path for a printing system, called kinematic media transport, is described in commonly assigned U.S. patent application Ser. No. 12/627,018 entitled “MEDIA TRANSPORT SYSTEM FOR NON-CONTACTING PRINTING” by Muir et al. Kinematic media transport is particularly well suited for printing apparatus that provide non-contact application of ink or other colorant onto a continuously moving medium. There are often dynamic considerations with such systems, in which changing conditions of the traveling print medium necessitate compensation by the media handling apparatus in order to maintain proper registration. The printhead of such a device, for example, selectively moistens at least some portion of the media as it courses through the printing system, which can impact media weight and stiffness, including cross-track stiffness, in a variable manner.
Depending on the relative configuration of rollers along the media path, an arrangement of castered and gimbaled rollers can be used to correct for cross-track drift caused by incorrect or variable cross-track web tensioning and thus help to prevent misalignment of the media. With respect to the orthogonal axes shown in
With the arrangement of
In many applications, the parasitic rotation about the y-axis shown in
Embodiments of the present invention address the problem of maintaining a uniform media web tensioning by providing a web tensioning apparatus that allows gimbal action but more effectively constrains caster rotation, so that parasitic caster rotation is reduced or eliminated, in turn reducing a tendency for unwanted cross-track motion of the moving media within the media transport system.
The schematic diagram of
In a first coupling 42, first end 52 of the roller shaft is rigidly connected to a first arm A1 that extends away from the roller axis to a first joint J1 that is mounted to the equipment frame 40, thereby coupling the first end 52 of the roller shaft to the frame 40 through arm A1 and joint J1. The roller shaft is thus free to rotate in all directions around joint J1.
A second coupling 44 and a third coupling 46 are at the opposite end of the roller 50 shaft from the first coupling 42. The second coupling couples the second end 54 of the roller shaft to the frame 40 by means of a second arm A2 and joints J2 and J3. Joints J2 and J3 individually allow arm A2 to pivot freely in all directions relative to the roller shaft 54 and the frame 40, respectively. In one embodiment, joint J2 is substantially in line with the roller 50 axis. The second end 54 of the roller shaft is rigidly connected to a third arm A3 that extends away from the roller axis to a fourth joint J4 that is coupled to the equipment frame 40, thereby coupling the second end 54 of the roller shaft to the frame 40 through arm A3; this coupling forming a third coupling. The fourth joint J4 is not rigidly coupled to the frame. Joint 4 is coupled to frame in a manner that allows the joint 4 to move in the z direction but constrains it to lie substantially in a plane defined by the first joint J1, the third joint J3, and a center point along the length of the roller shaft. This corresponds to constraining joint J4 to lie substantially in the X-Z plane passing through these three points. In the embodiment shown in
The length of first arm A1 is an offset distance D1, measured from the roller axis to the pivoting center of joint J1. The length of second arm A2 is a distance D2, the distance between the pivoting centers of joints J2 and J3. The length of third arm A3 is a distance D3, measured from the roller axis to the pivoting center of joint J4. Each of these distances is measured along the z axis. Distances D1, D2, and D3 are substantially equal to each other.
Still referring to
As arm A1 rotates, pivoting about joint J1 in one direction, arm A3, pivoting at joint J4, rotates in the opposite direction by a corresponding amount. Since distances D1 and D3 are equal, the rotations at the two ends of the roller shaft are equal. As a result rotation of the roller takes place about center point C, along axis G. Arms A2 and A4 cooperate in such a way that joint J4 is able to move slightly in the z direction, thereby forcing roller shaft end 54 to move in the z direction by the same amount as shaft end 52 does. Arm A2 is attached at one end to frame 40, and at the other end to the roller shaft. Thus, as arm A3 rotates, arm A2 also rotates. Rotation of arm A2 moves that end of the roller shaft in the z direction a distance equal to the equivalent z direction movement of the other end of the shaft as connected to arm A1 since distance D2 is substantially equal to distance D1. Thus, angular rotation about the y axis, or caster, is eliminated.
It can be observed that end of roller shaft 54 is free to move in the z direction by its connection to frame 40 through arm A4. One end of arm A4 is connected to arm A3 at joint J4. The other end of arm A4 connects to frame 40 through joint J5. Preferably joint J5 and joint J4 lie in a Y-X plane that is substantially perpendicular to the X-Z plane, which contains joints J1 and J3 and the center point C; the X-Y plane being parallel to the roller axis. Small rotations of arm A4 around joint J5 permit joint J4 to move small amounts in the z direction without significant motion in the y direction. As a result the fourth joint J4 is constrained to lie substantially in the plane defined by the first joint, J1, the third joint J3, and the center point C that is located along the length of the roller shaft.
The cooperative effect of arms A1 and A2 in preventing caster rotation can be more readily visualized by considering their equal lengths D1 and D2, respectively, with joints J1 and J3 both mounted to frame 40. Since joint J2 remains substantially in line with the roller shaft during gimbal rotation about the z axis, rotation about the y axis, or caster, is effectively constrained with this mechanical arrangement.
The perspective views of
Referring to
The second end 54 of the roller shaft is also coupled to the frame 40 by second coupling 44 that is made up of second joint J2, second arm A2, and third joint J3. In the embodiment of
The perspective view of
As shown in
In operation, unwanted z-direction movement of one end of roller 50 relative to the other end of the roller, corresponding to unwanted caster movement, is controlled by the combination of linkages on both sides of frame 40, while allowing gimbal movement at the same time. The combined interaction of these components provides equal foreshortening in the z direction, effectively compensating any rotation about the y-axis and constraining caster.
Since both the second arm A2 and the fourth arm A4 can rotate freely as a result of joints J2 and J3, and joints J4 and J5 respectively, the mounting of the second end of the roller shaft 54 by means of couplings 44 and 46 is insensitive to small variations in the spacing between the frame portions on the first and second end of the roller shaft. This simplifies installation of the gimbaled roller assembly and makes it insensitive to thermal expansion differences between the roller shaft and the frame.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
2454863 | Crocker | Nov 1948 | A |
2797091 | Fife | Jun 1957 | A |
3054547 | Alexeff et al. | Sep 1962 | A |
3069056 | Richards et al. | Dec 1962 | A |
3300114 | Jacobsen | Jan 1967 | A |
3373288 | Otepka et al. | Mar 1968 | A |
3436002 | Racine | Apr 1969 | A |
3452908 | Hindle et al. | Jul 1969 | A |
3595459 | Colombo | Jul 1971 | A |
4243167 | Sander | Jan 1981 | A |
5906305 | Knorr | May 1999 | A |
Number | Date | Country |
---|---|---|
0 803 458 | Oct 1997 | EP |
808 686 | Feb 1959 | GB |
Number | Date | Country | |
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20110206440 A1 | Aug 2011 | US |