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Delta 3D printers can significantly increase throughput in additive manufacturing by enabling faster and more precise motion compared to conventional serial-axis 3D printers. Further improvements in motion speed and part quality can be realized through model-based feedforward vibration control, as demonstrated on serial-axis 3D printers. However, delta machines have not benefited from model-based controllers because of the difficulty in accurately modeling their position-dependent, coupled nonlinear dynamics. In this paper, we propose an efficient framework to obtain accurate linear parameter-varying models of delta 3D printers at any position within their workspace from a few frequency response measurements. We decompose the dynamics into two sub-models–(1) an experimentally-identified sub-model containing decoupled vibration dynamics; and (2) an analytically-derived sub-model containing coupled dynamics–which are combined into one using receptance coupling. We generalize the framework by extending the analytical model of (2) to account for differing mass profiles and dynamic models of the printer’s end-effector. Experiments demonstrate reasonably accurate predictions of the position-dependent dynamics of a commercial delta printer, augmented with a direct drive extruder, at various positions in its workspace. Note to Practitioners—This work aims to equip high-speed 3D printers, like delta machines, with model-based controllers to complement their speed with high-accuracy. Due to the coupled kinematic chains of the delta, complex control methodologies, some of which require real-time state measurements, are often used to achieve satisfactory control performance. Our modeling approach provides an efficient methodology for obtaining accurate linear models without the need for real-time measurements, thus enabling practitioners to design linear model-based feedforward controllers to achieve the high throughput and accuracy desired in additive manufacturing (AM). The models we develop in this paper are intended for use with feedforward vibration compensation methods, which can be beneficial for both industrial-scale AM machines that have high-powered servo motors and feedback controllers, as well as consumer-grade AM machines which use stepper motors in feedforward control.
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Kinematic Analysis of a 5-DOF Positioner for Precision Additive Manufacturing
Additive manufacturing, as a viable industrial-production technology, requires multi-DOF positioning with high precision and repeatability for either the printer head, or the part being printed. In this paper we present a novel methodology to analyze the error propagation informing the design of a high-precision robotic 5-DOF positioner for applications in additive manufacturing. We designed our positioner through serial attachment of linear and rotational stages by comparing the precision of three different kinematic arrangements of stages. Within order to minimize positioning errors in Cartesian space, the kinematic sensitivity of the mechanisms end-effector relative to the maximum expected error of each joint was computed, and the kinematic configuration with smallest 6D positioning error at the end-effector was selected. The methodology employed in this paper for the error propagation analysis of serial kinematic chains has a great level of generality and can facilitate the design and optimization of a wide-class of multi-DOF positioners.
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- Award ID(s):
- 1828355
- PAR ID:
- 10310566
- Date Published:
- Journal Name:
- 44th Mechanisms and Robotics Conference (MR)
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1115/DETC2020-22600
