Example implementations relate to print media stacks. In some examples, a device may include a sheet channel to guide a sheet of print media within the sheet channel above and separated in a vertical direction from a stack of printed media when the sheet of print media exits a print path of a printer. The device may include a plurality of clamps to control alignment of the sheet of print media on the stack of printed media when the sheet channel moves outboard from the sheet of print media to allow the sheet of print media to fall onto the stack of printed media, wherein the plurality of clamps sequentially pin the sheet of print media to the stack of printed media from a middle portion of the sheet of print media outward.

Example implementations relate to print media stacks. In some examples, a device may include a sheet channel to guide a sheet of print media within the sheet channel above and separated in a vertical direction from a stack of printed media when the sheet of print media exits a print path of a printer. The device may include a plurality of clamps to control alignment of the sheet of print media on the stack of printed media when the sheet channel moves outboard from the sheet of print media to allow the sheet of print media to fall onto the stack of printed media, wherein the plurality of clamps sequentially pin the sheet of print media to the stack of printed media from a middle portion of the sheet of print media outward.

A three side trimmer has a trimming unit 1, an accumulating unit 3, a discharge unit 2 and a conveying mechanism 4 conveying trimmed booklets BK to the accumulating unit. The accumulating unit has a shelf 5 movable in a vertical direction, and a drive roller conveyor 7 on the shelf. The accumulating unit, in a mode, delivers the trimmed booklets to the discharge unit at every accumulation of a predetermined number of the trimmed booklets and, in another mode, accumulates the trimmed booklets without delivering.

An example system includes an advancement mechanism to drive print media into a stacking region, a movable media guide arrangement and a controller. The movable media guide arrangement includes a pair of opposing media guides to receive opposing edges of a print medium therein and a translation mechanism to move the opposing media guides between at least two positions, the at least two positions including a deployed position and a retracted position. The controller is to actuate the translation mechanism to move the opposing media guides into the deployed position when the advancement mechanism transports a print medium into the stacking region and to actuate the translation mechanism to move the opposing media guides to the retracted position to release the print medium.

An example system includes an advancement mechanism to drive print media into a stacking region, a movable media guide arrangement and a controller. The movable media guide arrangement includes a pair of opposing media guides to receive opposing edges of a print medium therein and a translation mechanism to move the opposing media guides between at least two positions, the at least two positions including a deployed position and a retracted position. The controller is to actuate the translation mechanism to move the opposing media guides into the deployed position when the advancement mechanism transports a print medium into the stacking region and to actuate the translation mechanism to move the opposing media guides to the retracted position to release the print medium.

A three side trimmer has a trimming unit 1, an accumulating unit 3, a discharge unit 2 and a conveying mechanism 4 conveying trimmed booklets BK to the accumulating unit. The accumulating unit has a shelf 5 movable in a vertical direction, and a drive roller conveyor 7 on the shelf. The accumulating unit, in a mode, delivers the trimmed booklets to the discharge unit at every accumulation of a predetermined number of the trimmed booklets and, in another mode, accumulates the trimmed booklets without delivering.

An example system includes an advancement mechanism to drive print medium into a stacking region, a clamping mechanism, and a controller. The clamping mechanism includes a trailing edge clamping arrangement in a trailing edge portion of the stacking region and at least one downstream clamping arrangement in a downstream portion of the stacking region, the downstream portion being downstream of the trailing edge portion. The controller is to sequentially actuate the trailing edge clamping arrangement and the at least one downstream clamping arrangement when the advancement mechanism transports a print medium into the stacking region.

An example system includes an advancement mechanism to drive print medium into a stacking region, a clamping mechanism, and a controller. The clamping mechanism includes a trailing edge clamping arrangement in a trailing edge portion of the stacking region and at least one downstream clamping arrangement in a downstream portion of the stacking region, the downstream portion being downstream of the trailing edge portion. The controller is to sequentially actuate the trailing edge clamping arrangement and the at least one downstream clamping arrangement when the advancement mechanism transports a print medium into the stacking region.

A sheet stacking apparatus includes a sheet alignment mechanism configured for aligning a sheet in a predetermined reference position; a gripper arrangement configured to grip the aligned sheet at at least two spaced-apart points of the sheet and to release the sheet on a stack; and a holder configured to hold the sheet in position on the stack while the gripper arrangement releases the sheet. The gripper arrangement is movable along a predetermined trajectory for moving the sheet from the reference position to a stacking position.

A sheet stacking apparatus includes a sheet alignment mechanism configured for aligning a sheet in a predetermined reference position; a gripper arrangement configured to grip the aligned sheet at at least two spaced-apart points of the sheet and to release the sheet on a stack; and a holder configured to hold the sheet in position on the stack while the gripper arrangement releases the sheet. The gripper arrangement is movable along a predetermined trajectory for moving the sheet from the reference position to a stacking position.