Patent Application
20090079127
The present disclosure relates generally to media pick and separation systems that are used in devices such as printers, copiers, scanners, facsimile machines and the like. These types of image-forming or image scanning devices typically include a media feeding mechanism that supplies individual sheets of print media (e.g. paper) onto which images are formed or from which images are scanned. Many such devices include a tray that stores an input stack of sheets of media, and a pick mechanism is used to pick the top sheet off of the input stack and advance the sheet to the feeding mechanism.
Many automatic document feeder systems are designed to pick the sheets in the input tray in a discrete manner. That is, the system picks the top sheet off of the stack and starts to feed that sheet into the paper path. Once the leading edge of the sheet trips a flag or sensor, the system changes modes to stop attempting to pick another sheet, and simply feeds this one sheet forward. This type of system produces a relatively large gap between the sheets. A large gap between sheets translates into lower throughput (fewer pages per minute) for the system.
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.
As noted above, automatic document feeding systems have been developed to pick individual sheets from an input tray. Some of these tend to leave a relatively large gap between subsequent sheets—in some cases greater than about 10″. Such large gaps between sequential sheets results in much lower throughput, giving the system a lower overall operational speed.
One way to reduce the gap between subsequent sheets of media is via a mode called “tailgate picking.” Tailgate picking involves picking sequential sheets with a much smaller fractional gap between sheets, rather than a gap that is closer to the full length of a sheet of media. Advantageously, the inventors have developed a new paper pick system that effectively implements tailgate picking to increase throughput, while at the same time reducing or avoiding multi-picking, torque spikes, and noise that can sometimes occur when more rapid paper picking is attempted.
One embodiment of the inventors' media pick system 110 is depicted in
Disposed on the media tray surface 114 below the pick roller 118 is a split retard pad, having two pad portions 126a, 126b, with a semi cylindrical pick roller trough 128 between them. This retard pad supports the media 124 and provides a surface that promotes effective picking of the sheets of media. However, in this new design, rather than having the retard pad directly below the pick roller, the retard pad is split into two pieces, with the trough between the pad portions. The materials of the pick roller and the retard pad can be chosen so that friction between the pick roller and the print media is higher than friction between the print media and the retard pad, which in turn is higher than friction between adjacent sheets of the print media. This helps the pick roller to effectively pick the last sheets of media from a stack throughout the life of the paper pick system.
While the embodiments shown and described herein include a semi cylindrical trough 128 for providing clearance around the pick roller 118 during a paper out condition, it is to be appreciated that other configurations can also be used to prevent contact of the pick roller with other surfaces when the pick arm is fully lowered. For example, the pick roller trough can have a shape other than semi-cylindrical. Indeed, rather than a trough with a curved bottom surface, the media support surface can simply be provided with a rectangular recess or depression. Alternatively, the media support surface can have an opening into which the pick roller drops, the opening having no bottom at all. Other configurations are also possible. Any structure associated with the media support surface that provides clearance around the pick roller when the pick arm is fully lowered, and which also meets other design aspects discussed herein, can be suitable.
The separated portions of the retard pad are spaced to provide lateral clearance with the sides of the pick roller, and the trough provides a forward clearance space for the pick roller. This space allows the pick roller to spin freely during a paper out condition, if the unit is still trying to pick with the pick arm in the fully lowered position. This can happen after the trailing edge of the last sheet of media has left the pick area, and can continue until the trailing edge leaves the scan zone. The trough provides a clearance zone for the pick roller when the pick arm is in the lowered position, so that the pick roller does not contact any other surface—either the retard pad or any other part of the media tray surface. This can prevent a large torque spike that might otherwise occur after the last page has left the pick zone if the system continues to try to pick with the high friction pick roller against the stationary retard pad.
A cross-sectional view of the pick roller 118 extended down into the pick roller trough 128 is shown in
Another cross-sectional view of the pick roller 118 positioned in the pick roller trough 128, this view taken at a right angle relative to the viewpoint of
At the same time, the lateral clearance between the pick roller 118 and the edges of the retard pad portions 126 cannot be so great that the print media will deflect down into the trough under the downward force of the pick roller, and thus effectively reduce the normal force between the pick roller and the media and contribute to mispicks. It is to be appreciated that the print media spans across the pick roller trough 128, between the split retard pad portions. When the media stack 124 is relatively thick, this span does not cause the print media to deflect significantly under the force of the pick roller. However, as sheets are successively picked and the media stack grows thinner, the stack will tend to bend more and more, potentially bowing away from the pick roller. To help reduce this effect, it is desirable that the clearance between the lateral sides of the pick roller and the sides of the trough/retard pad portions be kept below some maximum dimension that will help prevent excessive deflection or bowing of the print media when the stack is thin. Given likely manufacturing tolerances, the inventors have found that a design lateral clearance S in the range of about 2 mm is considered suitable to accomplish these objectives.
Another feature of this media pick system that contributes to effective tailgate picking is an overall reduction in the normal force of the pick roller against the media stack. During the pick process, it is desirable to maintain the magnitude of the normal force exerted onto the media stack by the pick roller within a predefined range so that the pick roller will properly engage the top sheet in the stack. If the magnitude of the normal force is too low, the pick roller will not be able to frictionally engage the top sheet. If the magnitude of the normal force is too high, multiple sheets may be fed and back tension can be created within the pick system drive mechanism. Additionally, the mechanism that rotates the pick arm can impose a parasitic drag on the printer system, which places a drag on motor torque.
In some pick systems the normal force between the pick roller and the top sheet of the media stack can be maintained in the range of about 100 g. This force level has been found to be suitable for the normal pick mode. However, in tailgate picking mode this normal force level tends to result in increased multi-picks (i.e. the system picks more than one sheet at a time). The inventors have found that a reduction in the pick roller normal force of around 40% (e.g. from about 100 g to about 60 g in one embodiment) helps to substantially reduce the incidence of multi-picks. Testing has shown that this force still has sufficient margin against no-picks in both normal and tailgate modes. In another embodiment the pick roller normal force can range from approximately 25 to 120 g.
Those of skill in the art will recognize that the pick roller normal force is inherently related to the coefficient of friction between the pick roller and the media through the equation F=μN, where N is the normal force, μ is the coefficient of friction, and F is the drive force that the roller can impart to the media. The drive force F has an influence on the robustness of the media picking system. Consequently, if there is a change in the coefficient of friction μ, a compensation in the normal force N can be provided to achieve the same drive force F. The inventors believe that a coefficient of friction in the range of about 1 to about 1.3 between the pick roller and the print media is suitable. In one embodiment the inventors have used materials for the pick roller that provide a coefficient of friction of about 1.25 between the pick roller and print media. EPDM elastomer material, cellular urethane, and silicone are considered suitable materials for the pick roller. Other materials can also be used.
Similarly, to maintain the desired hierarchy of frictional forces, the materials of the pick roller 118 and retard pad 126 can be selected to provide a frictional coefficient in the range of about 0.9 to about 1.3. The pick roller materials mentioned above are suitable in this respect, and can be used with a retard pad of cork to provide the desired level of friction.
Another design feature of this pick system relates to the separation pad 130. As noted above, some media pick systems include a separation roller that is narrower than the adjacent separation pad. The inventors have found that where the separation pad is wider than the separation roller, the edges of the roller can dig into the pad over time, because the roller is generally of a harder material than the pad. This leads to uneven wear of the separation pad, and also produces noise during the paper picking process, because of the uneven surfaces.
Shown in
Like the pick roller 118, the separation roller 120 can be of EPDM elastomer, cellular urethane, silicone, or other materials. The separation pad 130 can also be of silicone, though again, this material is generally softer than the material of the separation roller. Where the separation roller is of substantially the same material as the pick roller, the coefficient of friction between the separation roller and print media will be substantially the same as described above with respect to the pick roller. The materials of the separation roller and the separation pad are frequently chosen so that friction between the separation roller and the print media is higher than friction between the print media and the separation pad, which in turn is higher than friction between adjacent sheets of the print media. It is desirable that this hierarchy of frictional forces continue throughout the life of the paper pick system and in various environmental conditions. This helps promote consistent picking of the media, while also preventing multiple sheets from being picked. To provide the desired hierarchy of frictional forces, the coefficient of friction between the separation pad and separation roller can be in the range of from about 1 to about 1.3.
The present media pick system thus uses a narrower separation pad in combination with a reduced pick arm normal force and a split retard pad and pick roller trough to allow effective tailgate picking without torque spikes and pick errors. The inventors have found that a media pick system having this combination of features can significantly reduce the gap between subsequent pages and thereby increase throughput in a media picking system. In one embodiment, the system reduced the gap between subsequent sheets from about 10.7″ to about 2″, or by more than 67%. At the same time, this system reduces system noise and has a relatively low cost to implement.
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.
