Multi-material 3D-Printer for Rapid Prototyping
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but also very flexible materials, which are essential for the fabrication of soft robots. A
constraining guidance of the filament inside the extruder is an additional enhancement
to increase the quality of compressible elements. These components were outfitted with
cooling fans and connectors for the wiring (Fig. 1B). The backside of the tool forms the
“male interface” of the Maxwell coupling (Fig. 1D). Since the nozzle size can be selected
specifically for each task, it is possible to tune each print-head for its specific purpose.
Small or detailed structures can be printed with a smaller diameter than for example
support structures. This saves process time and cost. Like the coupling mechanism,
the print-heads do not rely on a precise fabrication. The attached parts and holders are
3D-printed and any resulting deviations can be compensated by defining an individual
offset along each axis for the mounted tools.
3 Characterization
In order to characterize the developed device, a series of specimens was designed and
fabricated. Hereby the focus was to evaluate the printer’s ability to handle a flexible
filament precisely and to combine it with traditional stiff materials, since these are
the ongoing challenges in soft robotic research. All the specimens were constructed
as chambers with an inlet to connect air supply and at least one flexible area that is
able to expand under pressure. For the stiff parts polylactid (PLA) was chosen whereas
thermoplastic urethane (TPU) served as a flexible material. All specimens were printed
with a 0.4 mm nozzle diameter, a layer height of 0.1 mm and a speed of 8 mm/s.
3.1 Pneumatic Actuator
To test the performance of the used extruder, a cuboid actuator was printed with relatively
thick and stiff bottom and top of 2.0 mm and thin, expandable sides of 0.8 mm thickness
(Fig. 3A). At the bottom a hole was added with a diameter of 3.3 mm, which was slightly
smaller than the connector to apply air pressure. The whole object was fabricated in one
print process using “Recreus FilaFlex TPU 82A” filament without any support structures.
The first layer of the ceiling was printed as hanging bridges from one side to the other.
Although flexible filaments are much less convenient to print unsupported structures,
the system is able to print them in a high quality. After a few slacking layers, a new
stable foundation was formed and the printer continued building a precise and tight top.
Next, the finished chamber was connected to a pneumatic test bench that precisely
regulates the applied air pressure. The first load of 1.0 bar confirmed the specimen to
be airtight and resilient. During a second test, the pressure was slowly increased and the
chamber continued to expand. Once pressure measured 2.5 bar, the connected silicon
tube bursted (Fig. 3B).
3.2 Pneumatic Finger
As a second test specimen, a series of the described pneumatic pillows was printed next
to each other with a spacing of 1 mm on top of a 7 mm thick backbone underneath,
pneumatically connecting the actuators by a groove in the backbone (Fig. 3C). The
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but also very flexible materials, which are essential for the fabrication of soft robots. A
constraining guidance of the filament inside the extruder is an additional enhancement
to increase the quality of compressible elements. These components were outfitted with
cooling fans and connectors for the wiring (Fig. 1B). The backside of the tool forms the
“male interface” of the Maxwell coupling (Fig. 1D). Since the nozzle size can be selected
specifically for each task, it is possible to tune each print-head for its specific purpose.
Small or detailed structures can be printed with a smaller diameter than for example
support structures. This saves process time and cost. Like the coupling mechanism,
the print-heads do not rely on a precise fabrication. The attached parts and holders are
3D-printed and any resulting deviations can be compensated by defining an individual
offset along each axis for the mounted tools.
3 Characterization
In order to characterize the developed device, a series of specimens was designed and
fabricated. Hereby the focus was to evaluate the printer’s ability to handle a flexible
filament precisely and to combine it with traditional stiff materials, since these are
the ongoing challenges in soft robotic research. All the specimens were constructed
as chambers with an inlet to connect air supply and at least one flexible area that is
able to expand under pressure. For the stiff parts polylactid (PLA) was chosen whereas
thermoplastic urethane (TPU) served as a flexible material. All specimens were printed
with a 0.4 mm nozzle diameter, a layer height of 0.1 mm and a speed of 8 mm/s.
3.1 Pneumatic Actuator
To test the performance of the used extruder, a cuboid actuator was printed with relatively
thick and stiff bottom and top of 2.0 mm and thin, expandable sides of 0.8 mm thickness
(Fig. 3A). At the bottom a hole was added with a diameter of 3.3 mm, which was slightly
smaller than the connector to apply air pressure. The whole object was fabricated in one
print process using “Recreus FilaFlex TPU 82A” filament without any support structures.
The first layer of the ceiling was printed as hanging bridges from one side to the other.
Although flexible filaments are much less convenient to print unsupported structures,
the system is able to print them in a high quality. After a few slacking layers, a new
stable foundation was formed and the printer continued building a precise and tight top.
Next, the finished chamber was connected to a pneumatic test bench that precisely
regulates the applied air pressure. The first load of 1.0 bar confirmed the specimen to
be airtight and resilient. During a second test, the pressure was slowly increased and the
chamber continued to expand. Once pressure measured 2.5 bar, the connected silicon
tube bursted (Fig. 3B).
3.2 Pneumatic Finger
As a second test specimen, a series of the described pneumatic pillows was printed next
to each other with a spacing of 1 mm on top of a 7 mm thick backbone underneath,
pneumatically connecting the actuators by a groove in the backbone (Fig. 3C). The