Multi-material 3D-Printer for Rapid Prototyping
47
1 Introduction
Soft robots are a key to a safe and natural interaction between machines and humans
(Rus and Tolley 2015). The replacement of stiff metal parts by flexible elements with the
ability to bend and compress predestines them for applications in a fragile environment
and/or for adaptive behavior. In contrast to their traditional relatives using bolts and
hinges, soft robotic parts can be designed to better resemble the natural designs of living
organisms. Therefore learning from nature and transferring those insights to artificial
systems is a useful approach to create lighter and more adaptive mechanisms (Coyle
et al. 2018). Like their natural role models such bioinspired or biomimetic systems are
usually based on the interaction of different materials integrated in a complex geometry.
Due to its wide range of useable substances and the offered high degree of design
freedom there has been a trend towards 3D-printing in the development of soft robots
(Gul et al. 2018). Previous studies have shown how different types of additive manufacturing can be used to fabricate solid and flexible structures, soft actuators (Zolfagharian
et al. 2016) or soft sensors (Muth et al. 2014). The limiting factor for developing more
advanced bioinspired soft robots is still the range of materials that can be used. This
is a challenge for both the field of material science and fabrication techniques (Trivedi
et al. 2008). So far the PolyJet technology, that applies and cures droplets of varying
photopolymer, is mostly used for multi-material prints (Khoo et al. 2015). However, they
suffer from high costs and a selection of materials limited to the stock inks distributed
by the supplier. On the other hand, more affordable and customizable 3D-printers are
usually designed to build visually impressive sculptures for private customers. In product information about these kind of machines the keyword “multi-material” is still used
synonymously for “multi-color” (of the same material) and the applied extrusion techniques like mixing and dual extruders have disadvantages for the challenges arising when
printing materials of different chemical composition.
In contrast to these systems, this study presents a novel multi-material 3D-printer with
on demand tool changing properties. The device is able to process multiple substances
within one print by switching between individual tools on runtime. The development
included the design of a suitable coupling mechanism, compatible print-heads and the
implementation of tool change procedure. The finished device was then used to create
several specimens in order to characterize the hardware and to test the reliability of the
process.
2 Printer Design
2.1 Printer Geometry and Work Principle
The printer design is based on a commercially available 3-axes system with a carriage
moving on the X/Y-plane and an independent Z-axis moving the build platform (Fig. 1A).
In contrast to commonly used Y/Z-systems this construction allows it to line up several
tools along the X-axis at the printer frame and to reach each of them with the carriage
without being affected by the Z-position of the build plate. The tools are safely docked on
two pins each with the coupling mechanism oriented towards the coupling of the carriage
(Fig. 1E/F). During tool pick up the carriage connects to the interface and pulls it off
47
1 Introduction
Soft robots are a key to a safe and natural interaction between machines and humans
(Rus and Tolley 2015). The replacement of stiff metal parts by flexible elements with the
ability to bend and compress predestines them for applications in a fragile environment
and/or for adaptive behavior. In contrast to their traditional relatives using bolts and
hinges, soft robotic parts can be designed to better resemble the natural designs of living
organisms. Therefore learning from nature and transferring those insights to artificial
systems is a useful approach to create lighter and more adaptive mechanisms (Coyle
et al. 2018). Like their natural role models such bioinspired or biomimetic systems are
usually based on the interaction of different materials integrated in a complex geometry.
Due to its wide range of useable substances and the offered high degree of design
freedom there has been a trend towards 3D-printing in the development of soft robots
(Gul et al. 2018). Previous studies have shown how different types of additive manufacturing can be used to fabricate solid and flexible structures, soft actuators (Zolfagharian
et al. 2016) or soft sensors (Muth et al. 2014). The limiting factor for developing more
advanced bioinspired soft robots is still the range of materials that can be used. This
is a challenge for both the field of material science and fabrication techniques (Trivedi
et al. 2008). So far the PolyJet technology, that applies and cures droplets of varying
photopolymer, is mostly used for multi-material prints (Khoo et al. 2015). However, they
suffer from high costs and a selection of materials limited to the stock inks distributed
by the supplier. On the other hand, more affordable and customizable 3D-printers are
usually designed to build visually impressive sculptures for private customers. In product information about these kind of machines the keyword “multi-material” is still used
synonymously for “multi-color” (of the same material) and the applied extrusion techniques like mixing and dual extruders have disadvantages for the challenges arising when
printing materials of different chemical composition.
In contrast to these systems, this study presents a novel multi-material 3D-printer with
on demand tool changing properties. The device is able to process multiple substances
within one print by switching between individual tools on runtime. The development
included the design of a suitable coupling mechanism, compatible print-heads and the
implementation of tool change procedure. The finished device was then used to create
several specimens in order to characterize the hardware and to test the reliability of the
process.
2 Printer Design
2.1 Printer Geometry and Work Principle
The printer design is based on a commercially available 3-axes system with a carriage
moving on the X/Y-plane and an independent Z-axis moving the build platform (Fig. 1A).
In contrast to commonly used Y/Z-systems this construction allows it to line up several
tools along the X-axis at the printer frame and to reach each of them with the carriage
without being affected by the Z-position of the build plate. The tools are safely docked on
two pins each with the coupling mechanism oriented towards the coupling of the carriage
(Fig. 1E/F). During tool pick up the carriage connects to the interface and pulls it off