A Layer-To-Layer Model and Feedback Control of Ink-Jet 3-D Printing

Ink-jet 3-D printing is a promising additive manufacturing technology with the potential for impacting a wide variety of industries. In typical ink-jet 3-D printing, the part is built up by depositing droplets layer upon layer in an open-loop manner, while curing each layer after it is deposited. Droplet and edge dimensions are typically predicted through extensive experimentation and are assumed to remain constant throughout the printing process. However, there is no guarantee of the consistent droplet shape and dimensions or the smoothness of the finished parts due to the inherent uncertainty in the process. To address this issue, we propose a model-based feedback control law for ink-jet 3-D printing that uses a height sensor for measuring profile height after each layer for determining the appropriate layer patterns for subsequent layers. Toward this goal, a model describing the relationship between height profile change and droplet deposition in the layer building process is first proposed and experimentally identified. Based on this model, a closed-loop layer-to-layer control algorithm is then developed for the ink-jet printing process. The proposed algorithm uses a model predictive control algorithm to minimize the difference between the predicted height and the desired height and the predicted surface unevenness after a fixed number of layers. We also present an extension of the algorithm for two-material printing, which can enable printing of complex 3-D geometry (by using a support material for overhang). Experimental and simulation results show that the algorithm is able to achieve more consistent shapes between layers, reduced edge shrinking of the part, and a smoother top layer surface.