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  • Christian LaRosa

This was Crawler, our earliest system.

Updated: Apr 15

Mechanizing a directed energy deposition (DED) printer to mimic nature's builders.


PHOENIX, AZ, USA - AUGUST 1, 2021 - Rosotics, Inc. (www.rosotics.com), creator of hyper-efficient metal additive manufacturing systems, details today the first 3D printer we've ever built, the Crawler mechanized printer. We believe in a future in which our capacity to manufacture in three-dimensions will expand significantly in scale, limited in no respect.


At inception, we sought out to create systems that would be capable of additively manufacturing structures much simpler, doing so at the same or better quality standards as practiced in industry. Prior to discovery of the Rapid Induction approach, which is designed to reduce the energy and material requirements of performance metal additive manufacturing, we experimented using the de-facto approach to large-scale production known as Directed Energy Deposition (DED). This approach is characterized by utilizing a laser mounted against a robotic arm to liquefy and lay down metal wire, also ejected from the arm, to construct objects in free space. This process initially held our focus as it is able to produce relatively large solid objects, and it existed at the time as a well-researched starting point for experimentation in metal additive manufacturing.


Prior to the design of our core platform, a bio-inspired machine targeted at proving the simplest concept, that the demanding act of metal 3D printing could even take place from a self-contained and autonomous system, underwent a design cycle. This was the necessary first step that had to be proven before advancing to the active development of our core platform today. While not an ideal, or performance-oriented system, it would be capable of self-contained (that is, no additional infrastructure required) directed energy deposition; as well as fully autonomous operation. This machine was referred to internally as 'Crawler', and was designed capable of rudimentary production using a 17-gauge aluminum wire feedstock in tandem with two fiber lasers. It exists, to date, as the only machine ever built that is able to conduct the DED process entirely self-contained. Crawler would be comprised of mostly off-the-shelf components, excluding that of structure and firmware in order to bootstrap costs and keep time to manufacture short.



The procedural methodology of Crawler was to begin with a small industrial precision 6-DOF robotic arm, fit it with a custom designed end affector to function as an injector, deliver to this injector feeds of aluminum wire feedstock and gaseous argon, affix radially to the injector the terminators of two separate fiber lasers, power these components using vey high-capacity lithium polymer and sealed lead acid batteries, and affix all of these components to an all terrain spider-like frame with visual sensory and advanced computational capabilities. The result was a large mechanized robot with eight legs and a central body element. The central body element was comprised of three segments, the Canopy, the Core, and the Trunk. The body of Crawler would be entirely 3D printed of ABS Plastic, and printed in segments using several specifically sourced large format 3D printers. The body segments would be treated in an acetone vapor bath and painted a polished finish. The process of structural printing for all of the required structural segments, joint fittings, and internal supports would take seven months across three large-format printers. Fully integrated, the large machine would weigh 42.24 kg (93 lbs), 3.7 ft in length and 2.3 ft in width.



The eight leg segments, each containing three actuable joints, utilized 24 high-torque ASME-04B high-torque servo motors, costing $1,674 and accounting for 12.72 kg of powertrain weight. The structure of each leg contained two main structural bodies - the proximal body, connecting to the Core segment, and a distal body, contacting the floor. The proximal body actuated lateral to the Core segment by means of a servo motor for positioning of the leg segment forward and backward. A triangular strut existed to interface the proximal body with the distal body, by means of a second and third servo, and was reinforced against the distal body by means of a distal pylon in tandem with reinforcement against the proximal body by means of a proximal pylon. For assembly purposes, these structures were mated and then closed with plate caps interfacing with each structure. The second servo actuated the distal body upward or downward against the proximal body, while the third servo actuated the distal body angularly. These servos affixed directly with the proximal and distal bodies, assembly aided by an opening in the side of each body removed and replaced for this purpose, known as the proximal and distal plates. These plates contained cylindrical segments each affixed to the interfacing strut, and closed with a proximal/distal plate cap. Both the proximal and distal bodies incorporated on the interior of their structures channels for wiring to be guided from the distal body towards the Core segment. The proximal body affixed to the Core segment using the first servo, reinforced by an anchor structure on the underside and a collection of anchor rods. Wiring of each servo enters the Core segment using exterior holes in the structure. Each joint was soldered and then jacketed under heat with a UL224 flame-retardant polymer heat-shrink. The wiring of each leg terminates in a female XT90 connector. In total, the leg connectome contains 96 soldered joints terminating in eight XT90 connectors for quick disconnect with power storage.



We knew in order for a radically simple large-scale manufacturing system to work, the system would require full, complete autonomy. Not only would complete autonomy be required, but this autonomy would need to come at little power draw or hardware footprint. A system capable of processing visual data, as well as perceiving a world of depth, existed at the time as a 'stereo camera' (a similar approach as the human visual system, employing two eyes). For computation and sensory, we therefore incorporated an Nvidia Jetson AGX Xavier (0.65 kg), as well as two Stereolabs ZED Mini stereo cameras. The Xavier board was housed at the front of the Core segment, vented by a hexagonal pattern above on the head structure. The ZED Mini stereo cameras were mounted at the front and rear of the Core segment. Four HRLV-MaxSonar-EZO ultrasonic sensors were mounted above, in the Canopy segment, for lateral sensory. The 24 servo motors of the Legs segment were controlled by Jetson Xavier through means of a slaved Arduino Mega 2560 microcontroller, interfaced with an expansion shield to accommodate all of the servo connections necessary. Jetson Xavier conducted computational operations on the visual streams as they were recorded live, to conduct simultaneous localization and mapping (SLAM), among other functions, near real time. Jetson Xavier was selected as the computational workhorse for this machine due to delivering up to 32 TOPS of AI performance by means of a 512-core Volta GPU inclusive of tensor cores. The platform also utilized an 8-core ARM v8.2 64-bit CPU, with 32 GB of 256-bit LPPDDR4X RAM, and 32 GB of eMMC 5.1 storage. The 512-core Nvidia Volta GPU incorporates 512 CUDA cores and 64 Tensor cores, delivering 32 TOPS of deep learning performance at INT8 and 16 TFLOPS at FP16. This platform additionally contained all of the necessary ports to interface with the system's auxiliary sensors. The ZED line of stereo cameras were selected, because by utilizing a stereo-based vision stack, they are able to natively sense depth and perform other important algorithms. They record real-time video up to a resolution of 2.2K, up to 100 frames per second. Each video feed was encoded in h.264 codec. The camera units also incorporated an accelerometer, gyroscope, and inertial measurement unit (IMU). Each camera was operated at a data rate of 800 Hz, a pose update rate of 100 Hz, a pose translation drift of 1.0%, a pose rotation drift of 0.013 deg/m without loop correction, and with 6-DoF visual-inertial stereo data collection for SLAM. Each lens of each camera was set to an aperture of ƒ/2.0. Each camera interfaced to Jetson Xavier using USB 3.0, weighing 62.9 g. The two ZED cameras provided frontal and rear visual sensory for SLAM, as well as imagery for deep learning computation. The four ultrasonic sensors mounted to the canopy on both left and right provided non-visual sensory for SLAM. A third camera of the thermal sense, an Adafruit AMG8833 IR breakout was incorporated at the rear for thermal visual data collection.



At the front and rear of the Core segment existed manually soldered arrays of 5mm white LED flat-lensed diodes, providing lighting in low-light conditions. These LED arrays were each soldered to resistors and in turn to 5V relay modules, interfacing with the Mega 2560 microcontroller. The LED arrays were each jacketed under heat with a UL224 flame-retardant polymer heat shrink, with a total of 119 soldered joints.



A lightweight aluminum pressure vessel of welding specification was painted and incorporated directly under the canopy, housing pressurized argon at 153 bar, and plumbing transferred this Argon using a set of valves and regulators to the rear of the Core segment, where it was ejected from the exterior through tubing and delivered to the injector. This gaseous argon was continually blown over the work spot from the injector during operation at a constant flow rate to serve as localized shielding, in order to combat the effects of oxidation. The injector, affixed to the end effector of MECA500, also incorporated fiber terminators from two separate fiber lasers. These fiber lasers, two Coherent FAP800-L-16W 830NM, supplied heat for the DED process and were themselves cooled using two Arctic Freezer 11 LP-100W CPU Coolers. Laser beams were delivered to the injector using laser-grade fiber optic cables. The interior of the Core segment was further aided in airflow using an Arctic P12 Silent 120mm case fan and an Arctic P8 SIlent 80 mm case fan. The fiber lasers were powered independently using two Enersys (Hawker) Cyclon 2V/25 Ah sealed lead acid batteries (3.36 kg). Mega 2560, the LEDs, the case fans, and other auxiliary electronic components were powered using four Enegitech 9V 1.2 Ah lithion-ion batteries. Power was delivered among all of these elements appropriately using clips, connectors, buck converters, and other interfaces. To power the 24 servo motors of the Leg segment, which require great power to maintain their rated holding torque, four Turnigy 20,000 mAh 6S 12C lithium-polymer battery packs (10.52 kg) were incorporated into the Core segment for the powertrain. 1 battery was allocated each to two legs, respectively. Feedstock was housed within the structure on a spool, and transferred by means of NEMA 14 0.9 deg high-precision stepper motors, driven by DRV8825 drivers. Plasti-dip rubber coating aerosol was utilized to aid in feedstock travel. A 17 gauge aluminum wire was utilized, and delivered to the injector out of the exterior using PTFE tubing. Each of these components described was supported within the structure by an aluminum underframe, which was JB-welded to the physical body and fused together. The underframe further reinforces the body against axial loads and directional tension.


For maintenance and assembly, the exterior structure was removable using several sections. The Trunk Segment is a plate affixed over MECA500, mounted at an angular sense against a mounting structure of the Core Segment. The Canopy Segment is an exterior structure that fit over the length of the Core segment and the argon vessel.



Procedurally, Crawler would first rest on the belly of the Core segment, with legs raised. Each servo motor was positioned during integration so that this was their 'idle' state. When powered on, the legs actuated downward, in order to lift the body off the ground. Vision and sensory systems would perform simultaneous localization and mapping (SLAM) in order to map the environment and prepare to navigate throughout it. Crawler would identify characteristics within the environment deemed 'ideal' for printing, such as level metallic substrate surfaces and open space through which to maneuver, and then position itself based on these features for printing. For printing, the arm on the rear would actuate into position, and then execute machine code for motion, translated from a 3D model (a cartesian coordinate frame was utilized, similar to traditional 3D printers, only executed using a 6-DOF robotic arm), and each layer of fluid aluminum feedstock would be deposited under gaseous argon shielding flow from the injector. The robot would conclude by returning to its home position, where the legs would lower it onto its belly and thereafter lift up off the ground to idle, before powering off. During this entire process, no human is involved in the state flow.



A range of support components were acquired during this development process, such as the actual large-scale 3D printers to produce the body at low cost, custom enclosures for these printers, and their respective parts and hardware, as well as safety components and other pieces of hardware. The end weight of Crawler totaled to 42.24 kg (93 lbs), 44" in length and 28" in width. The cost of development and construction, including the auxiliary costs mentioned above, totaled to $5,799.81, closing in December of 2020. An exclusion exists in the procurement of the MECA500 robotic arm, which was rented during the testing cycle directly from Mecademic.



Production


We were able to cut costs significantly in production of the this early machine by utilizing 3D printing in advanced polymers, producing the parts in-house. This also allowed for a high degree of adaptability and rapid iteration. We were able to reduce costs by purchasing off-the shelf components and combining them to reach a desired effect; an example is sourcing industrial fiber laser diodes at low power and concentrating each of them to the work point, rather than spending tens of thousands for an integrated single fiber laser of similar power output. We were able to begin, conduct, and finish the entire development cycle from conception over a span of months, rather than traditionally longer time scales.



Capability


Crawler is able to perform the directed energy deposition (DED) print process, in a rudimentary capacity, using a 17 gauge wire aluminum feedstock. We do not consider it to be a representative performance system however, as the Rapid Induction process iterates heavily upon the approach and associated characteristics of directed energy deposition (DED). Machine learning capabilities of Crawler were comprehensive, and were contained to the onboard computational structure enabled by Jetson AGX Xavier. Classical simultaneous localization and mapping (SLAM), image recording, and autonomous movement formed the foundation of Crawler's firmware element. Crawler's operation was framed for relative simplicity; the hardware however limited by its core process - and DED's associated complexity. For this reason, Crawler was a partial step in line with our mission, though inconsequential. We were satisfied primarily in that a DED system could however function fully self-contained, fully on its own power and cognition.




Impact


We believe in a future in which our capacity to manufacture in three-dimensions can expand significantly in scale, limited in no respect. Crawler, our earliest machine, served as a crucial first step in answering the question of self-contained additive manufacturing. Its successors, tracing their lineage all the way back to Crawler, will provide a fundamental increase in capability when compared to industry's state-of-the-art approaches to large-scale production. Our purpose built additive manufacturing process, Rapid Induction Printing, streamlines the number of inputs required to sustain performance metallurgy, and is viewed as a major leap to achieving true simplicity.


For more information on Rosotics, please view our published documentation on this process at www.rosotics.com/documentation.


About Rosotics, Inc.

Rosotics produces hyper-efficient metal additive manufacturing solutions that solve tougher problems in industrial engineering. A pioneer of large-scale additive manufacturing, we enable today’s manufacturers to produce structures that are normally difficult or impossible to create.


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Press Contact

Austin Thurman

Project Manager

austin@rosotics.com