Printable Hydraulics

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Printable Hydraulics: A new method for fabricating force-transmission elements within robots

Multi-material additive-manufacturing techniques offer a compelling alternative to conventional rigid and soft robot fabrication techniques, allowing materials with widely varying mechanical properties to be placed at arbitrary locations within a structure, and enabling design iterations to be rapidly fabricated with trivial effort. This capability enables complex composite materials with new bulk properties, and in contrast to virtually all other fabrication techniques, the incremental costs of additional design complexity when using additive manufacturing are zero. We have exploited this feature to co-fabricate solids and fluids within the same 3D-printed structure, demonstrating a new capability for transmitting force within 3D-printed robots: Printable Hydraulics.


ICRA 2016 Paper - Printable Hydraulics: A Method for Fabricating Robots by 3D Co-Printing Solids and Liquids

ICRA Video Submission
CSAIL Promo Video

Automated assembly of integrated robotic structures

Printed Hydraulics Overview
Printed Hydraulics Overview
Printed Hydraulics Overview
Printed Hydraulics parts are fabricated layer-by-layer, by depositing adjacent droplets of liquids and solids

This method, based on inkjet deposition of photopolymers and non-polymerizing fluids, can achieve resolutions better than 100μm, allowing the fabrication of complex channels for fluid routing and capillary structures for selectively distributing hydraulic pressure to regions of the assembly with precisely graded elasticity, enabling prescribed movements in response to pressure changes. Control of complex composite assemblies fabricated in this manner is simplified because the working fluid is incompressible; because the solid and fluid regions are fabricated together, there is no need to purge air bubbles or remove support material. The key idea of this approach to robot fabrication is to automate the assembly of complete robotic structures. By reducing or eliminating assembly steps, this method breaks the connection between design complexity and fabrication complexity, allowing complex designs to be fabricated with trivial effort.

Basic Transducer Unit: the Bellows

Basic Bellows
This example was fabricated in a single-step, with the working fluid already embedded inside. No materials need to be added or purged
Bellows FEA
Finite-element analysis modeling allows the material deformation and stress to be estimated

The achievable feature sizes of drop-on-demand inkjet printers are too coarse to print sliding seals; they would leak. As a result, conventional piston designs are not practical. An alternative design using a bellows avoids the need to have seals entirely. As the pressure inside the bellows increases the material deforms and the bellows extends. This deformation can be modeled using finite element modeling tools to ensure that the stress and strain in the printed material does not exceed allowable limits. The bellows design is inherently modular: if greater actuator extension is required additional folds can be added, and if larger force is required (for a given input fluid pressure) the cross-section of the bellows can be increased.

Fabricating a robot in a single step

Applications to Soft-Robotics

A single-sided bellows fabricated with soft rubbery material (Shore A28) creates a "finger"
The same finger, connected to a bellows, creating a sealed system that is printed in a single step
Two fingers, connected in an antagonistic configuration make a soft gripper
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