Jonathan D. Hiller

Automatic Design and Manufacture of Soft Robots

We present the automated design and manufacture of static and locomotion objects in which functionality is obtained purely by the unconstrained 3-D distribution of materials. Recent advances in multimaterial fabrication techniques enable continuous shapes to be fabricated with unprecedented fidelity unhindered by spatial constraints and homogeneous materials. We address the challenges of exploitation of the freedom of this vast new design space using evolutionary algorithms. We first show a set of cantilever beams automatically designed to deflect in arbitrary static profiles using hard and soft materials. These beams were automatically fabricated, and their physical performance was confirmed within 0.5-7.6% accuracy. We then demonstrate the automatic design of freeform soft robots for forward locomotion using soft volumetrically expanding actuator materials. One robot was fabricated automatically and assembled, and its performance was confirmed with 15% error. We suggest that this approach to design automation opens the door to leveraging the full potential of the freeform multimaterial design space to generate novel mechanisms and deformable robots.

Design and analysis of digital materials for physical 3D voxel printing

Purpose – Virtual voxels (3D pixels) have traditionally been used as a graphical data structure for representing 3D geometry. The purpose of this paper is to study the use of pre‐existing physical voxels as a material building‐block for layered manufacturing and present the theoretical underpinnings for a fundamentally new massively parallel additive fabrication process in which 3D matter is digital. The paper also seeks to explore the unique possibilities enabled by this paradigm.Design/methodology/approach – Digital RP is a process whereby a physical 3D object is made of many digital units (voxels) arranged selectively in a 3D lattice, as opposed to analog (continuous) material commonly used in conventional rapid prototyping. The paper draws from fundamentals of 3D space‐filling shapes, large‐scale numerical simulation, and a survey of modern technology to reach conclusions on the feasibility of a fabricator for digital matter.Findings – Design criteria and appropriate 3D voxel geometries are presented ...

Tunable digital material properties for 3D voxel printers

Purpose – Digital materials are composed of many discrete voxels placed in a massively parallel layer deposition process, as opposed to continuous (analog) deposition techniques. The purpose of this paper is to explore the wide range of material properties attainable using a voxel‐based freeform fabrication process, and demonstrate in simulation the versatility of fabricating with multiple materials in this manner.Design/methodology/approach – A representative interlocking voxel geometry was selected, and a nonlinear physics simulator was implemented to perform virtual tensile tests on blocks of assembled voxels of varying materials. Surface contact between tiles, plastic deformation of the individual voxels, and varying manufacturing precision were all modeled.Findings – By varying the precision, geometry, and material of the individual voxels, continuous control over the density, elastic modulus, coefficient of thermal expansion, ductility, and failure mode of the material is obtained. Also, the effects...

Multi material topological optimization of structures and mechanisms

Multi-material 3D-printing technologies permit the freeform fabrication of complex spatial arrangements of materials in arbitrary geometries. This technology has opened the door to a large mechanical design space with many novel yet non-intuitive possibilities. This space is not easily searched using conventional topological optimization methods such as homogenization. Here we present an evolutionary design process for three-dimensional multi-material structures that explores this design space and designs substructures tailored for custom functionalities. The algorithm is demonstrated for the design of 3D non-uniform beams and 3D compliant actuators.

A Vacuum-Based Bonding Mechanism for Modular Robotics

We explore vacuum as bonding force for modular robotics. Vacuubes are a set of modules that propagate vacuum across their interfaces in order to generate adhesive forces to form and hold structures. We use analog circuits to simulate vacuum transients and understand critical design parameters and then validate these insights in experiments. A 49-module structure that employs vacuum bonding is demonstrated. We conclude that vacuum offers a relatively strong, simple, reliable, and power-efficient connection principle.

Evolutionary Design and Assembly Planning for Stochastic Modular Robots

A persistent challenge in evolutionary robotics is the transfer of evolved morphologies from simulation to reality, especially when these morphologies comprise complex geometry with embedded active elements. In this chapter we describe an approach that automatically evolves target structures based on functional requirements and plans the error-free assembly of these structures from a large number of active components. Evolution is conducted by minimizing the strain energy in a structure due to prescribed loading conditions. Thereafter, assembly is planned by sampling the space of all possible paths to the target structure and following those that leave the most options open. Each sample begins with the final completed structure and removes one accessible component at a time until the existing substructure is recovered. Thus, at least one path to a complete target structure is guaranteed at every stage of assembly. Automating the entire process represents a step towards an interactive evolutionary design and fabrication paradigm, similar to that seen in nature.

Constructing controllers for physical multilegged robots using the ENSO neuroevolution approach

Evolving controllers for multilegged robots in simulation is convenient and flexible, making it possible to prototype ideas rapidly. However, transferring the resulting controllers to physical robots is challenging because it is difficult to simulate real-world complexities with sufficient accuracy. This paper bridges this gap by utilizing the Evolution of Network Symmetry and mOdularity (ENSO) approach to evolve modular neural network controllers that are robust to discrepancies between simulation and reality. This approach was evaluated by building a physical quadruped robot and by evolving controllers for it in simulation. An approximate model of the robot and its environment was built in a physical simulation and uncertainties in the real world were modeled as noise. The resulting controllers produced well-synchronized trot gaits when they were transferred to the physical robot, even on different walking surfaces. In contrast to a hand-designed PID controller, the evolved controllers also generalized well to changes in experimental conditions such as loss of voltage and were more robust against faults such as loss of a leg, making them strong candidates for real-world applications.

Microbricks for Three-Dimensional Reconfigurable Modular Microsystems

This paper explores the design of “microbricks”-interlocking microscale building blocks that can be used to assemble and reconfigure 3-D structures on a regular lattice. We present the design and fabrication of a space-filling rotation and flip-invariant 500-μm microbrick architecture suitable for 3-D assembly. We describe the design considerations used to optimize mechanical, fabrication, and assembly properties of the components and the finished structures. The final brick geometry was fabricated using two different fabrication techniques: Silicon bricks were micromachined out of silicon, and SU-8 polymer tiles were built up in a three-layer process. The resulting bricks were characterized, and proof-of-concept structures comprising ten bricks were assembled to demonstrate the physical interlocking and compatibility between the two materials. We suggest that the presented interlocking geometry could serve in the future to fabricate passive and active modular macroscale structures from microscale components.

Morphological evolution of freeform robots

We demonstrate the evolution of locomoting amorphous robots composed of multiple materials. Research in evolutionary robotics has traditionally been limited to morphologies comprising rigid and discrete components, such as links connected with rotational or linear joints and actuators. In the continuous robots presented here, actuation is accomplished by periodic volumetric expansion and contraction of one or more materials composing the body of the robot. The challenges of representing evolvable multi-material freeform shapes and evaluation (simulation) of the resulting soft bodies are discussed. Several genotypic representations are explored which use a level-set threshold to generate the material distribution in the phenotype. Soft body simulation of the robot is accomplished using a relaxation algorithm to model the dynamics of the resulting amorphous machines under the actuation material expansion, gravity forces, and non-linear ground friction. These results open the door to a new design space that more closely mimics the freeform, amorphous and continuous nature of biological systems.