Media-sheet stacking systems

1. A media-sheet stacking system for stacking media sheets on an output tray for a device, the stacking system comprising:

a kicker to advance a media sheet along the output tray by pushing a trailing edge of the media sheet exiting the device, wherein the kicker is moveable between an extended position and a retracted position, the kicker to retract from the extended position to the retracted position responsive to the trailing edge of the media sheet exiting the device, and after the kicker has retracted from the extended position to the retracted position, the kicker is to extend from the retracted position to the extended position to push the media sheet onto the output tray;

an output roller to push the media sheet to the output tray;

a sensor to sense presence of the media sheet, wherein the kicker is to retract from the extended position to the retracted position responsive to the sensor ceasing to detect the presence of the media sheet;

a movable element arranged to face the output tray across a space receiving media sheets exiting the device; and

a drive mechanism to drive the movable element in a direction of advance of the media sheet along the output tray.

2. The media-sheet stacking system of claim 1 , wherein the movable element comprises a belt facing the output tray.

3. The media-sheet stacking system of claim 2 , wherein the drive mechanism is configured to move the belt in the direction of advance of the media sheet at a speed faster than a speed of advance of the media sheet along the output tray.

4. The media-sheet stacking system of claim 3 , further comprising a biasing mechanism to bias the belt towards a stack of media sheets on the output tray.

5. The media-sheet stacking system of claim 4 , wherein the biasing mechanism comprises a set of arms each having one end mounted to rotate about a pivot point and another end to push the belt towards the stack of media sheets on the output tray.

6. The media-sheet stacking system of claim 1 , wherein the kicker has a curved profile, and the curved profile of the kicker is to move along a curved path as the kicker is moved between the extended position and the retracted position.

7. The media-sheet stacking system of claim 6 , wherein the kicker has a tip shaped to push the trailing edge of the media sheet exiting the device into a position away from an exit path from the device.

8. The media-sheet stacking system of claim 7 , further comprising guide ribs positioned at an exit of the device to cooperate with the kicker to define a channel to guide media sheets exiting the device.

9. The media-sheet stacking system of claim 1 , wherein the output tray has an exit end remote from the device, and a shape of the exit end is curved or bent to avoid formation of a platform for accumulation of curling media sheets.

10. The media-sheet stacking system of claim 9 , further comprising a set of suspended weights hanging proximate the exit end of the output tray to bend over ends of media sheets stacked on the output tray when the ends of media sheets extend beyond the exit end of the output tray.

11. The media-sheet stacking system of claim 9 , wherein the length of the output tray is set to avoid matching any of a set of standard lengths specified for media sheets.

12. The media-sheet stacking system of claim 1 , wherein when the kicker is in the retracted position the media sheet is allowed to drop towards a surface of a stack of media sheets on the output tray.

13. The media-sheet stacking system of claim 12 , wherein when the kicker is in the extended position the kicker pinches a top surface of the stack of sheets.