  This paper presents the integration of a feedback control loop during the
printing of a plastic object using additive manufacturing. The printed object
is a leaf spring made of several parts of different infill density values,
which are the control variables in this problem. In order to achieve a desired
objective stiffness, measurements are taken after each part is completed and
the infill density is adjusted accordingly in a closed-loop framework. The
absolute error in the stiffness at the end of printing is reduced from 11.63%
to 1.34% by using a closed-loop instead of an open-loop control. This
experiments serves as a proof of concept to show the relevance of using
feedback control in additive manufacturing. By considering the printing process
and the measurements as stochastic processes, we show how stochastic optimal
control and Kalman filtering can be used to improve the quality of objects
manufactured with rudimentary printers.
