1. Soft Robotic: Fabrication and Manufacture Process
Daniel Nakhaee-Zadeh, James Kinch and Jun W. Kow
Supervisors: Ali Alazmani and Peter Culmer
Soft Robotics is a new kind of robotics that instead of relying on traditional
mechanic elements such as motors or gears, it uses soft and easy deformable
materials.
The use of soft robotics is increasingly becoming very popular in the medical
field for its low impact in patients
The fabrication of these robots using soft materials is highly complicated as
most of the time the whole system have to be crafted in a single element and
modular fabrication is not possible.
The objective of this research is to investigate new fabrication techniques
for pneumatic actuated soft robots
but also improve the methodology
of previous fabrication techniques.
The project is focused in PneuNets
soft robotics, that consist on soft
material structures containing
chambers in which pressured air flows.
The melted soft material is extruded by a 3D printer in different layers, while
the material slowly cures at the room temperature. Using a 3D printer very
complex and intricate structures are possible to be made. However, right now
this method lacks of compatible soft materials.
Linear Soft Actuator
3D printing (FDM)
Lost Wax Casting
Overview
It is the most accessible fabrication method, as it allows to produce simple
soft actuators at a low cost and without the need of complicated techniques.
Below, there are some of the actuators develop using the moulding technique.
On the other hand, moulding lacks of precision compared to other techniques
like soft lithography or 3D printing. Hollow and complex internal shapes are
difficult to achieve using moulding.
Shear-Thickening Fluid
Moulding
This method uses wax as moulding material, usually as a core to create hollow
pieces. The surface finish of the wax and its flexibility allows for the fabrication
of hollow and complicated shapes with high levels of reproduction and with a
low cost.
This method was develop for the fabrication of Ecoflex ™ soft actuators,
however other platinum base silicones can also be compatible. The wax core
can be easily created by melting it and pouring it on an acrylic mould. Other
benefits of this method is that the wax after its use can be melted out of the
mould and recycle.
Other objective of the project was to create a oscillatory linear actuator that
could serve as a brush to sweep material from the inside of a human body,
where there is a limited amount of space for movement. The design is based
on a unit block that contains two symmetric chambers that can be
pneumatically actuated independently to obtain a oscillatory movement. The
initial design was created using Solid Works and optimized for its objective
using the Solid Works Simulation tool.
Using the specifications of SolidWorks, the actuator was fabricated by pouring
Ecoflex 00-30 in a laser cut acrylic mould. A dynamic test was perform on the
actuator to characterise its motion and deformation. The test revealed that
the working frequency and shape were adequate. However, the lack of
bending stress on the base and the high deformation on the top wasn’t the
expected.
Shear-thickening fluids react to shear stress by changing viscosity. This means
that depending on the force that is applied to the fluid it can be a hard
material or a really soft one. The specific fluid used on this research was a
mixture of fumed silica with polypropylene glycol with a ratio of 9:1. The
objective of studying this types of fluids is to apply them into the limiting
layers of soft robots, allowing them to bend and twist. For its characterization
the fluid was introduce into an Ecoflex container and it was tested using a
linear stage actuator controller. This part is not yet concluded and further test
will be needed.
Figure 1. Multigait soft robot
Figure 5. 3D printed tentacle using fused deposition modelling
Figure 2. Multiple soft actuators develop in the research project using Ecoflex ™ material.
Figure 3 and 4. Wax core used to develop a soft actuator (left) and the same core use to create a hollow cylindrical
structure in Ecoflex (Right)
Figure 6. Simulation of the brush actuator prototype using Solid Works Simulation tool. This represents the
expected motion of the actuator
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Conclusion
Overall this research has been able to compile great amounts of information on
different aspects of the fabrication for soft robots. The lost wax casting
introduce in the research group will enable to generate complicated hollow
shapes for future projects. Furthermore, the research has been a great
evaluation exercise of the design limits and boundaries for soft robotic devices.
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Figure 7. Final product of the brush actuator concept being tested.
School of Mechanical
Engineering
Faculty of Engineering