Patent Application
20090033025
The present disclosure relates generally to inkjet printing systems. In some types of inkjet printers the imaging system is held stationary while the print media is held on a shuttle plate or platen and swept through the printzone. This type of system offers some speed advantages over some other printers that move both the inkjet pens and the media. However, this architecture requires that the media be held down upon a shuttle plate in order to maintain accurate PPS (pen to paper spacing) and accurate control of the media.
The print media is often held to the shuttle plate by vacuum pressure. When the printing operation is complete, the media is ejected from the shuttle plate using mechanical rockers. In order to eject the print media from the shuttle plate, the rockers must overcome the downward vacuum pressure force exerted upon the media. For larger media sizes, this force can become quite large (since force equals pressure times area) and cause the rockers to deflect. In such cases the media may end up breaking the vacuum and lifting off the plate, but the stored energy in the rockers can cause a slingshot effect, which causes loss of control of the media and can ultimately lead to media jams.
Various features and advantages of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the present disclosure, and wherein:
Reference will now be made to exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended. Alterations and further modifications of the features illustrated herein, and additional applications of the principles illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of this disclosure.
The present disclosure relates generally to inkjet printing systems, particularly those in which the imaging system is held stationary and the print media is swept through the printzone. An example of this type of printing system is shown in
In these types of systems the print media is frequently held down upon the shuttle plate 16 by vacuum pressure. A closer perspective view of a portion of the shuttle plate assembly 12 is shown in
When the printing operation is complete, the print media is ejected from the shuttle plate 16 using a mechanical device, such as mechanical rockers. Shown in
In order to eject the print media from the shuttle plate 16, the rockers 24 must overcome the downward vacuum force exerted upon the print media. For larger media sizes, this force can become quite large and cause the rockers to deflect when they are caused to press up against the print media. For example, for a piece of 5″×7″ print media and a vacuum pressure of about 4.3 psi, the total hold-down force can be about 135 pounds. In such cases the media may end up breaking the vacuum and lifting off the plate, but the stored energy in the rockers can cause a slingshot effect, which can cause loss of control of the media and can lead to media jams in the offloading system (not shown, mentioned above).
Some possible approaches to this problem include lowering the overall system vacuum pressure by throttling the vacuum supply system, or by adding a vent to atmosphere inside the manifold. This approach can reduce the overall hold-down strength and reliability of the media handling mechanisms, and can result in media transfer errors. Moreover, a reduced vacuum approach may not provide sufficient strength to suck down “curled”, or cockled media. Another possible approach is to temporarily turn off the vacuum supply system when it is desired to eject the media. This, however, can be difficult to time precisely, and can require additional cycle time to actuate a valve or turn off a vacuum pump to vent the manifold.
The inventors have developed a system in which vacuum pressure in the manifold is vented simultaneously with lifting of the media. This lowers the lifting force required by the rockers and results in smooth media ejection. Several side views of one embodiment of a media shuttle plate assembly 12 having a rocker actuated vacuum relief valve system are shown in
Also associated with the proximal end 36 of at least one of the rockers 24 is a valve seat 40 that opens and closes the vacuum release valve 32. The mechanical rockers are spring-loaded to stay in a retracted position during printing operations. This condition is shown in
Referring to
It should be recognized that valves of various types and configurations can be used for the vacuum release valve. For example, while a linear valve is shown in the figures, a rotary valve or other type of valve could also be used, and mechanically linked to the rocker arms for actuation when the rocker arms move to eject the print media.
As the rockers 24 continue to rotate, the vacuum pressure continues to be released, and the rockers begin to lift the media 50 from the shuttle plate 16. This condition is shown in
As the rockers continue to rotate, as shown in
A variety of materials can be used for the various components of this media ejection system. The shuttle plate can be made of aluminum or similarly rigid material to ensure flatness under vacuum pressure. The manifold and rocker arms can be of suitable polymer materials, such as LCP and acetal plastic. The use of polymer materials helps reduce the weight and cost of the system. The vacuum release valve can also be of polymer material. Where vacuum pressures are relatively low, this valve can be configured without a special elastomer seal material if desired. In one embodiment the inventors have used a conical plastic valve seat with no special seal material. Though this configuration can allow a small amount of leakage, this leakage is small compared to the vacuum pump's flowrate capability, and the pump has been sufficient to overcome this leakage. It is anticipated that where higher vacuum pressures are used a special valve seal can also be provided.
This media ejection system and method enables the use of a relatively high amount of hold down vacuum pressure, which improves media hand-off reliability (i.e. the reliability of transferring media to and from the shuttle plate 16). It also provides a “built-in” method of controlling the venting process because the same motion that causes ejection of the print media also vents the vacuum system. There are no additional motions or actuations needed for both of these actions.
The system and method disclosed herein thus simultaneously vents vacuum pressure in a shuttle plate manifold and lifts the media for ejection using a single mechanism. The vacuum release valve is directly mechanically linked with the rockers that eject print media from the moveable shuttle plate in the ink jet printer, so that the mechanical action that lifts the media simultaneously releases the vacuum pressure, thus substantially equalizing pressure above and below the media and reducing the lifting force required. This lower lift force can enhance media control and reduce wear on the rockers and other parts.
It is to be understood that the above-referenced arrangements are illustrative of the application of the principles disclosed herein. It will be apparent to those of ordinary skill in the art that numerous modifications can be made without departing from the principles and concepts of this disclosure, as set forth in the claims.
