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The delta robot can reach higher speeds than traditional serial-axis machines used in fused filament fabrication 3D printing. However, like serial machines, delta printers suffer from undesirable vibration at high speeds which degrades the quality of fabricated parts. This undesirable vibration has been suppressed in serial printers using linear model-inversion feedforward control methods like the filtered B-splines (FBS) approach. However, techniques like the FBS approach are computationally challenging to implement on delta 3D printers because of their coupled, position-dependent dynamics. In this paper, we propose a methodology to address the computational bottlenecks by (1) parameterizing the position-dependent portions of the dynamics offline to enable efficient computation of the model online, (2) computing models at sampled points (instead of every point) along the given trajectory, and (3) employing QR factorization to reduce the number of floating-point arithmetic operations associated with matrix inversion. In simulations, we report a computation time reduction of up to 23× using the proposed method when compared to using the computationally expensive exact LPV model—all while maintaining high tracking accuracy. Accordingly, we demonstrate significant quality improvements on parts printed at various positions on a commercial delta 3D printer using our proposed controller compared to a baseline alternative, which uses an LTI model from one position. Acceleration measurements during printing show that the improvement in print quality of the proposed controller is due to vibration reductions of up to 39% when compared to the baseline controller. [ABSTRACT FROM AUTHOR]

Feedrate optimization (FO) and servo error pre-compensation (SEP) are often performed independently to improve the accuracy and speed, respectively, of computer-controlled manufacturing machines. However, this independent approach leads to excessive tradeoff between speed and accuracy. To address this issue, the authors have proposed a new concept of simultaneous FO and SEP (or FOSEP) where SEP is integrated into FO, yielding large reductions in motion time without sacrificing positioning accuracy relative to independent FO and SEP. However, in their prior work, the authors used linear programming to achieve FOSEP resulting in the following: (i) inaccuracy in enforcing nonlinear constraints and (ii) poor computational efficiency for long toolpaths. To address these two problems, this paper proposes a new approach for FOSEP using windowed sequential linear programming (SLP). The use of SLP improves the accuracy of FOSEP in enforcing nonlinear constraints; however, it lowers the computational efficiency of FOSEP. Windowing addresses the problem of low computational efficiency by applying SLP to FOSEP in small overlapping batches. A downside of windowed SLP is that it may lead to infeasibility in the optimization. This problem is resolved by smoothly switching between the optimal solution obtained using windowed SLP and a backup conservative solution in case of impending infeasibility. The proposed windowed SLP with smooth switching approach for FOSEP is validated in simulations where it significantly improves the accuracy and computational efficiency of FOSEP while guaranteeing feasibility. The practical benefits of the proposed approach for FOSEP is demonstrated in experiments on a 3D printer where it achieves up to 25% reduction in cycle time without sacrificing printing quality relative to the conventional approach of independent FO then SEP, both applied to a long toolpath. [ABSTRACT FROM AUTHOR]

Servo error pre-compensation and feedrate optimization are often performed independently to improve the accuracy and speed of manufacturing machines. However, this independent approach leads to unnecessary trade-offs between productivity and quality in manufacturing. This paper proposes a novel linear programming approach for combined servo error pre-compensation and feedrate optimization, subject to contour error (tolerance) and kinematic constraints. The incorporation of servo error pre-compensation into feedrate optimization allows for faster motions without violating tolerance constraints. Experiments carried out on a 3D printer and precision motion stage are respectively used to demonstrate up to 43% and 47% reduction in cycle time without compromising part quality using the proposed approach compared with the independent approach. [ABSTRACT FROM AUTHOR]