RepRap 3D Printer
Author: Rodolfo Antonio Salido Benítez
Completion Date: Summer, 2015
Software: Simplify 3D, Arduino, Printrun
Place of Creation: Califronia Institute for Biomedical Research. (Calibr)
Techniques: Computer aided design & manufacturing, additive manufacturing, and micro controller programming.
Materials: Bill of Materials
RepRap
A RepRap 3D printer is a self-replicating rapid prototyping device that uses Fused Filament Fabrication (FFF) methodologies to physically reproduce 3D models from thermoplastic materials. RepRap machines are mindfully designed to be able to self replicate by manufacturing their own parts to be assembled by people into other RepRap machines. All the parts that the machine cannot make for itself are designed to be easily source-able and highly standardized.
Founded by Adrian Bowyer, the RepRap project is often referenced as one of the major catalysts for the popularization of desktop 3D printers. The idealized RepRap machine was conceived as a self-replicating autonomous robot with a mutualistic relationship with humans; the latter would assist the self replicating process of the machine by providing assemblage of parts in exchange of additive manufacturing services. Bowyer believed that to maximize the "fecundity" of the machine, its source should be available for free, allowing users to own copies of the machine and to use it to fabricate replicates. Consequently, the RepRap project was licensed under a GPU's General Public License.
Mini Kossel
A modified Mini Kossel, a RepRap variant, was manufactured by 3D printing necessary plastic components in Polylactic Acid (PLA) using a Robo R1+ commercial desktop 3D printer. All non-printable components were independently sourced via online retailers like Robotdigg, Amazon, McMaster Carr, and e3D-online.
The electronic components of the machine are comprised by the widely adopted RepRap Arduino Mega Pololu Shield (RAMPS 1.4) and the open hardware Arduino Mega micro-controller. Motion is driven by NEMA 17 motors coupled with Pololu stepper driver boards. The machine features an e3D v6 hot-end with a bowden extruder that's fed by a geared NEMA motor. Because of the highly modular design of the RAMPS 1.4 shield, the Mini Kossel was later fitted with an LCD screen and SD card reader for interfacing. The machine runs on Rich Cattel's marlin firmware, which allows it to automatically calibrate for an unleveled printing bed and correct for imperfect frame geometry. The personally manufactured Mini Kossel is capable of printing PLA with an empirically tested resolution of 200 microns in the Z dimension, and 35 microns in the XY dimension. It has a cylindrical printing volume 160 mm diameter by 210 mm in height.
I chose to build a delta 3D printer as opposed to a cartesian printer simply because I was fascinated by the kinematics behind the design of the former. While a cartesian printer moves in the XYZ coordinate system by assigning X, Y, and Z motion commands to motors that drive translational movement in their respective planes independent of each other, a delta printer effects movements in the XYZ coordinate system by orchestrating movements of three different motors that depend on each other. In oversimplified terms, ignoring various constant offsets, three different motors that move carriages in vertical towers mechanically form three right triangles, where one corner of each triangle meets in one common effector head. All three triangles have fixed hypotenuse lengths but variable side lengths which can be modified in precise quantities to allow for the calculated placement of the effector head in the XYZ coordinate system. Thus, for a delta printer to carry out 3D printing instructions, inverse kinematic calculations have to take place in order to translate XYZ displacement into coordinated vertical tower movements. For instance, a cartesian printer trying effect a 10 mm movement in the Y direction only needs to use one motor dedicated to the Y plane, but a delta printer needs to move all three motors in an orchestrated fashion to effect the same movement.
Diagram of one mechanical triangle illustrated with variables and constants used to calculate inverse kinematics. Image from Delta Robot Kinematics by Johann C. Rocholl
3D printed projects presented in this portfolio, with the exception of those described under the Device Prototyping page, were manufactured using this 3D printer, which demonstrates that a personally manufactured self replicating machine can be used to materialize a wide variety of ideas with applications that range from simple ergonomic work-stages to complex mechanical devices that interface with the human body.