Chilean Researchers Experiment with Climbing Koala 3D Printer

University of Chile researchers Maximiliano Vélez, Efrén Toala, and Juan Cristóbal Zagal have developed a new angle for fabrication in construction, developing a novel machine that pairs a climbing robot with a 3D printer. Releasing their findings in the recently published ‘Koala 3D: A continuous climbing 3D printer,’ the authors attempt to streamline methods for fabrication of large-scale objects, creating hardware that can ‘continuously navigate along an object being fabricated.’

3D printers are being relied on more regularly in construction projects today and those using materials like concrete, from developing art and furniture to making foam panels, to creating concepts for entire 3D printed villages. Hardware is typically restricted to making objects smaller than their own structures, although the authors point out that one of the benefits of 3D printing is in the ability to make parts that are ‘not substantially smaller than the volume of the complete machine.’

With the new concept of a machine that prints while moving along the object being fabricated (and not just a part being created from a 3D printing platform), the researchers delve further into additive manufacturing processes integrated with:

• Autonomous collaborative robotic assembly
• Vertical slipform construction
• Truss forming machines for aerospace applications

The authors originally came up with a concept for the printer header part and the climbing part, mean to work via a pair of robotically actuated clamps, with the lower mechanism at the bottom of the printer body and the upper mechanism moving between the upper and bottom. Small servo motors were used for clamping due to their compact, lightweight properties, and well as offering high torque. Clamping was performed in an open-loop motion.

Koala 3D mounted on its printing base. Upper inlet: Printing and reanchoring phases of the fabrication process

“The printer can be decomposed into two major subsystems. One is the vertical climbing stage for reanchoring, precise vertical motion during printing, as well as carrying the electronics,” explained the authors. “The other subsystem is the x-y positioning stage for moving the printer extruder. This stage also carries the material impulsion system. The following subsections describe the design of each subsystem.”

Details of the parts of final design of Koala 3D printer. (a) Base of the printer part supports the y-rack, y-rails and the yendstop switch. (b) The y-carriage supports the y-motor, the x-rack, the x-rails and the x-endstop. (c) The x-carriage supports the x-motor and the extruder. (d) Servo base are secured to lower and central carriages of the climbing part. Each servo subassembly drives a leadscrew that transmits force to the clamp (e) Jaws in LCC and CCC with two retractile wheel permits guide the movement of the robot and retract when the clamps must anchor (f) Lower clamping carriage LCC hold lifting motor and lead screw. (g) Central clamping carriage CCC has a nut that joins to the lead screw from LCC (h) The upper carriage is not motorized and has a counterweight for displacing the center of mass.

The positioning system is meant to be more robust, offering improvements over typical 3D printers, with a stage covering extruder motion range of 45mm x 45mm on the x-y plane.

“We expected to produce vertical beams having a sectional area of 30mm x 30mm with this motion span. The extra motion span (50% larger on every dimension) was intended to allow the extruder to purge outside the printing area as well as potentially introduce some features on the surface of the produced beam,” explained the authors.

“It was observed that most x-y positioning stages used on 3D printers rely on motion belts driven by timing pulleys. The driving motor is often kept aside from the motion rails and one extra pulley is used to transmit power to the stage. The design was too voluminous for our purposes. Therefore, we opted to position the driving motors in the middle of the rails and transmitted power by means of pinion and rack mechanism. This also required fewer components.”

Due to streamlined design, lighter weight and ‘reported performance,’ the J-Head E3D extruder was chosen for the new 3D printing concept.

“We used the freely available Bowden material impulsion design which is a material impulsion unit located apart from the printing head,” said the authors. “The material is guided into the extruder using a plastic tube.”

a) Longitudinal cut front view. 1 Upper carriage 2 x-y stage 3 Central carriage 4 Printed column 5 Lower clamping carriage b) Free body diagram when Koala is in printing process. In this stage the central clamping carriage is holding the whole machine while the lower clamping carriage is guiding the movement through the column. 6 Material feeder 7 Counterweight 8 Leadscrew 9 Control board c) C-C cut view. Free body diagram of central clamping press during the printing stage (d) D detail. Forces on CCC during the printing process.

A set of eleven sample beams were 3D printed in different sizes, varying from 350 mm to 850 mm, with the addition of one smaller part also fabricated.

“A broad range of experiments were conducted to characterize and understand the proposed concept. It was demonstrated that 3D printing is possible using the proposed printing-reanchoring-printing scheme. Experiments and performance evaluations were executed at the desktop scale with materials commonly used for 3D printing (PLA plastic),” concluded the researchers.

“We identified a theoretical limit to the height of objects produced using these materials. It was caused by the reduced mechanical strength of PLA but not the fabrication process itself. The use of stronger materials will certainly serve to extend these limits. We detected, characterized, and proposed solutions for three important problems in climbing 3D printers. The problems are (1) the machine drop after reanchoring, (2) the structural oscillation at high aspect ratios, and (3) the initial alignment between part and base. Addressing these problems will be important in developing autonomous machines that can climb along the same structures they produce.”

(a-c) Examples of using a micrometer to measure machine drop during reanchoring. The machine is initially suspended by the CCC. Subsequently, (a) The LCC engages and CCC disengages. (b) Subsequent motion of the CCC results in an increased drop. (d) An example of producing a large beam. Supporting video 2 shows the machine in action while printing this beam.

In the future, the authors also plan to simplify the mechanism used for anchoring, as well as create a more basic design to eliminate the use of counterweight. Along with those plans, they also plan to refine the climbing system with less actuators and less weight for better performance.

New 3D printers are continually being created and specifically for the large-scale from concrete formwork to aircraft parts to studying effects like spatter. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.