[0001] In stapling finishers such as known e.g. in printing systems, sheets can be collected
to buffer sheets to keep productivity while stapling. A stapling action takes some
time to perform and it is preferred that the print engine is not obliged to slowdown
to compensate for this stapling time. It will be clear from the following that although
the invention is described with a stapler, the invention can be applied in any printing
system where sheets are to be buffered for some time, such as printing systems configured
to perform stapling, binding, punching, gluing or the like finishing operations. Printing
systems may be e.g. inkjet based, hot melt based, toner based or a sheet processing
apparatus where no marking material is applied.
[0002] A known method of buffering works by stopping the first sheet in a nip and letting
a second sheet slide over the first sheet in a second nip as displayed in figure 1.
The first sheet is fed and stopped by nip 2. Then the second sheet is fed and collated
with sheet 1. After some time the two sheets are transported together.
[0003] For this to work, the friction between rollers and sheets needs to be sufficiently
larger than the inter-sheet friction. If this is not the case, then the resulting
alignment between sheets in undefined. Furthermore the principle causes smearing of
toner on the sheets.
[0004] Two alternative solutions are hereinafter described
Embodiment A
[0005] As soon as the second sheet reaches nip 1 the transport both sheets together as displayed
in figure 2. In this method slip between the sheets is prevented by allowing an overlap
of the sheets after collecting. The steps are shown in figure 2.
[0006] The first sheet is fed (A) and stopped in nip 2. Then a second sheet is fed (B).
When the second sheet reaches nip 1, both nips are activated and the sheets are transported
together, with overlap (C). Now the sheets can possibly be stopped, for example to
wait for another action to finish (D). Finally the sheets can be transported together
(E), after which they may need to be realigned.
Embodiment B
[0007] A variation on this in displayed in figure 3 where nip 1 is opened while the first
sheet is laying still and closed again to transport the two sheets together Embodiment
B is much like embodiment A, but in this alternative embodiment, nip 1 is never stopped
but is opened, e.g. by a voice coil or any other way for opening the nip.
[0008] The first sheet is fed (1) and stopped in nip 2. Nip 1 is opened, then a second sheet
is fed (2). When the second sheet has passed nip 1, but has not yet reached nip2,
nip1 is closed and nip 2 is activated (3). The sheets are transported together, with
overlap. Now the sheets can possibly be stopped, for example to wait for another action
to finish (4). While stopped, nip 1 is opened again. Finally the sheets can be transported
together (5), after which they may need to be realigned.
1. Method for inline buffering of sheets in a sheet processing apparatus, comprising
the steps of
- feeding a first sheet into a transport nip
- feeding a subsequent sheet overlapping onto the first sheet while the transport
nip is engaged with the first sheet, such that the relative velocity of the subsequent
sheet with respect to the first sheet is substantially zero such that scraping of
the subsequent sheet over the first sheet is minimized.
2. Method as described here above and shown in figures 2 or 3.
3. Apparatus configured to perform the method according to any one of claims 1 or 2.
