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Copier Paperpath Control: Overview.
The objective of this project is to study fundamental principles
for introducing advanced sensor, actuation and decision making
methodologies into the design of media handling systems for the
next generation of copier machines. Many problems in copiers are
due to malfunctions of the media handling system. These include
paper jams, machine shutdowns due to impending paper jams (soft
shutdown), damage to the original documents and poor finishing
of the copy job.
These problems are further amplified by a demand for:
- Wider range of media:
Consumers want the ability to copy on and from an ever wider variety
of media, ranging from transparencies to envelopes, labels and
paperboard. In addition, environmental concerns ask for the
accomodation of recycled paper. Compared to fresh paper, recycled
paper often has a higher contaminant content, lower stiffness and
less well controlled properties.
- Job complexity:
There exists an increasing demand for duplex printing, color printing
and in the number of finishing steps for copy jobs (like collation
and stapling).
- Throughput:
The high forces necessary in high speed printing tend to increase the
likelihood of a paper jam and deterioration of accuracy.
The project addresses the above from a mechatronics point of view.
Current copier designs function mainly in an open loop fashion, assume
standard sheet properties and environmental conditions and are rather
conservative in order to achieve robustness. Only small position error
corrections can be made before the image is transferred onto the sheet.
Adding extra sensors and actuators, in combination with an intelligent
control strategy, can lead to increased robustness and throughput.
More specifically, we propose to split up the paperpath (which
transports sheets from the feeder to the image transfer unit)
into multiple, independently driven sections. This approach allows
us to adjust the relative positions of sheets, as they are transported
along the paperpath, by varying the section velocities. Optical sensors,
that detect the presence of a sheet, are used to measure sheet
positions.
The main control challenge follows from the fact that the resulting
system is a switched, or also, hybrid system. As sheets move through
the paperpath, their velocity is determined by different sections,
and therefore actuators. In this way, the continuous mapping from
system inputs to state evolution switches discretely between various
system descriptions. This behavior makes it no longer possible
to apply standard, linear control techniques.
As a first approach, a hierarchical, hybrid control strategy is currently
being implemented. For this purpose, an experimental setup was
built using standard copier parts. The results will allow us to
identify the main disturbances present in the system and further
refine future control strategies. Also, the field of hybrid systems,
as it gains in maturity, may allow us to apply and contribute a more
systematic, theoretical approach. (Carlo Cloet, August 1999)
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