Freeform Assembly Planning

Abstract

3D printing enables the fabrication of complex architectures at multiple length scales by automating large sequences of additive steps. The increasing sophistication of printers, materials, and generative design promises to make geometric complexity a non-issue in manufacturing; however, this complexity can only be realized if a design can be translated into a physically executable sequence of printing operations. We investigate this planning problem for freeform direct-write assembly, in which filaments of material are deposited through a nozzle translating along a 3D path to create sparse, frame-like structures. We enumerate the process constraints for different variants of the freeform assembly process and show that, in the case where material stiffens via a glass transition, determining whether a feasible sequence exists is NP-complete. Nonetheless, for topologies typically encountered in real-world applications, finding a feasible or even optimal sequence is a tractable problem. We develop a sequencing algorithm that maximizes the fidelity of the printed part and minimizes the probability of print failure by modeling the assembly as a linear, elastic frame. We implement the algorithm and validate our approach experimentally, printing objects composed of thousands of large-aspect-ratio sugar alcohol filaments with diameters of 100-200 µm.Note to Practitioners-Extrusion-style 3D printers typically pattern material in a series of 2D layers, but they can be also be programmed to deposit material along 3D paths in a "freeform" fashion. However, programming a printer to operate in this way requires consideration of constraints related to collision and stability. For large designs, finding an optimal or even feasible plan with respect to these constraints requires automated planning. We address a hard version of this problem in which any joint in the frame can only support one cantilever at a time. We develop an exact algorithm that maximizes the robustness of the printing plan, and validate it by printing complex freeform designs. The assembly planner allows the freeform process to be applied to arbitrarily complex parts, with applications ranging from tissue engineering and microfluidics at the micrometer scale, to vascularized functional materials and soft robots at the millimeter scale, to structural components at the meter scale. This approach removes a major bottleneck in the workflow for freeform assembly, allowing scientists and engineers to automatically translate complex freeform designs into optimal printing plans.

Robotic additive construction of bar structures: Unified sequence and motion planning

“…By rigidly committing to a partial ordering on the construction sequence, these algorithms are incomplete. Gelber et al [13] presented a complete forward search algorithm for a 3-axis 3D printer that constrains the deformation of the structure but does not address higher-DOF systems. Choreo was the first extrusion planning system that uses a robot manipulator to make robotic extrusion planning for arbitrary topologies possible [18].…”

Bioprinting: Prospects, considerations and challenges for application in South African clinical environments

“…Generative design is a computer-controlled human-guided design process that utilises a biomimicry approach to building stable, efficient structures that could assist greatly in bioprinting, considering the micron scales of biological detail. [40] The levels of scale and organisation in biological tissues and organs cannot be ignored and is an important factor in bioprinter development and selection, as the XYZ resolution in current printing processes is controlled by both the printer as well as the bioink.…”

Automated sequence and motion planning for robotic spatial extrusion of 3D trusses

“…Related problems In the context of 3D printing in bioengineering, Gelber et al presented a heuristic backtrack searching algorithm to generate printing sequence to enable micro-scale spatial 3D printing on a purpose-built isomalt 3D printer [18]. They were the first to identify that joint positioning errors are caused by beam compliance and include it as a cantilever constraint in the sequence searching process [18] [19]. This finding influenced the nodal printing orders routing part of the sequence planning module presented in this work (section 3.3.2).…”

“…This assignment has recently proven to be critical for the physical execution of spatial extrusion due to the molten joint's incapability to resist bending moment and elastic recoil effect [19]. Gelber et al introduce a cantilever constraint to their extrusion planning algorithm to address this problem: new elements cannot be connected to node p, if any previously printed element connected to p is cantilevered [18]. A relaxed version of this constraint is used here to route the nodal printing order: starting from the node with larger degree (number of connected elements) is preferred.…”