Cagdas D. Onal

Meshworm: A Peristaltic Soft Robot With Antagonistic Nickel Titanium Coil Actuators

This paper presents the complete development and analysis of a soft robotic platform that exhibits peristaltic locomotion. The design principle is based on the antagonistic arrangement of circular and longitudinal muscle groups of Oligochaetes. Sequential antagonistic motion is achieved in a flexible braided mesh-tube structure using a nickel titanium (NiTi) coil actuators wrapped in a spiral pattern around the circumference. An enhanced theoretical model of the NiTi coil spring describes the combination of martensite deformation and spring elasticity as a function of geometry. A numerical model of the mesh structures reveals how peristaltic actuation induces robust locomotion and details the deformation by the contraction of circumferential NiTi actuators. Several peristaltic locomotion modes are modeled, tested, and compared on the basis of speed. Utilizing additional NiTi coils placed longitudinally, steering capabilities are incorporated. Proprioceptive potentiometers sense segment contraction, which enables the development of closed-loop controllers. Several appropriate control algorithms are designed and experimentally compared based on locomotion speed and energy consumption. The entire mechanical structure is made of flexible mesh materials and can withstand significant external impact during operation. This approach allows a completely soft robotic platform by employing a flexible control unit and energy sources.

Self-folding with shape memory composites

Origami-inspired manufacturing can produce complex structures and machines by folding two-dimensional composites into three-dimensional structures. This fabrication technique is potentially less expensive, faster, and easier to transport than more traditional machining methods, including 3-D printing. Self-folding enhances this method by minimizing the manual labor involved in folding, allowing for complex geometries and enabling remote or automated assembly. This paper demonstrates a novel method of self-folding hinges using shape memory polymers (SMPs), paper, and resistive circuits to achieve localized and individually addressable folding at low cost. A model for the torque exerted by these composites was developed and validated against experimental data, in order to determine design rules for selecting materials and designing hinges. Torque was shown to increase with SMP thickness, resistive circuit width, and supplied electrical current. This technique was shown to be capable of complex geometries, as well as locking assemblies with sequential folds. Its functionality and low cost make it an ideal basis for a new type of printable manufacturing based on two-dimensional fabrication techniques.

An Origami-Inspired Approach to Worm Robots

This paper presents an origami-inspired technique which allows the application of 2-D fabrication methods to build 3-D robotic systems. The ability to design robots as origami structures introduces a fast and low-cost fabrication method to modern, real-world robotic applications. We employ laser-machined origami patterns to build a new class of robotic systems for mobility and manipulation. Origami robots use only a flat sheet as the base structure for building complicated bodies. An arbitrarily complex folding pattern can be used to yield an array of functionalities, in the form of actuated hinges or active spring elements. For actuation, we use compact NiTi coil actuators placed on the body to move parts of the structure on-demand. We demonstrate, as a proof-of-concept case study, the end-to-end fabrication and assembly of a simple mobile robot that can undergo worm-like peristaltic locomotion.

Peristaltic locomotion with antagonistic actuators in soft robotics

This paper presents a soft robotic platform that exhibits peristaltic locomotion. The design principle is based on the unique antagonistic arrangement of radial/circular and longitudinal muscle groups of Oligochaeta. Sequential antagonistic motion is achieved in a flexible braided mesh-tube structure with NiTi coil actuators. A numerical model for the mesh structure describes how peristaltic motion induces robust locomotion and details the deformation by the contraction of NiTi actuators. Several peristaltic locomotion modes are modeled, tested, and compared on the basis of locomotion speed. The entire mechanical structure is made of flexible mesh materials and can withstand significant external impacts during locomotion. This approach can enable a completely soft robotic platform by employing a flexible control unit and energy sources.

Robot self-assembly by folding: A printed inchworm robot

Printing and folding are fast and inexpensive methods for prototyping complex machines. Self-assembly of the folding step would expand the possibilities of this method to include applications where external manipulation is costly, such as micro-assembly, mass production, and space applications. This paper presents a method for self-folding of printed robots from two-dimensional materials based on shape memory polymers actuated by joule heating using embedded circuits. This method was shown to be capable of sequential folding, angle-controlled folds, slot-and-tab assembly, and mountain and valley folds. An inchworm robot was designed to demonstrate the merits of this technique. Upon the application of sufficient current, the robot was able to fold into its functional form with fold angle deviations within six degrees. This printed robot demonstrated locomotion at a speed of two millimeters per second.

Design and control of a soft and continuously deformable 2D robotic manipulation system

In this paper we describe the design, fabrication, control, and experimental validation of a soft and highly compliant 2D manipulator. The arm consists of several body segments actuated using bi-directional fluidic elastomer actuators and is fabricated using a novel composite molding process. We use a cascaded PI and PID computation and novel fluidic drive cylinders to provide closed-loop control of curvature for each soft and highly compliant body segment. Furthermore, we develop algorithms to compute the arms forward and inverse kinematics in a manner consistent with piece-wise constant curvature continuum manipulators. These computation and control systems enable this highly compliant robot to autonomously follow trajectories. Experimental results with a robot consisting of six segments show that controlled movement of a soft and highly compliant manipulator is feasible.

Soft Mobile Robots with On-Board Chemical Pressure Generation

We wish to develop robot systems that are increasingly more elastic, as a step towards bridging the gap between man-made machines and their biological counterparts. To this end, we develop soft actuators fabricated from elastomer films with embedded fluidic channels. These actuators offer safety and adaptability and may potentially be utilized in robotics, wearable tactile interfaces, and active orthoses or prostheses. The expansion of fluidic channels under pressure creates a bending moment on the actuators and their displacement response follows theoretical predictions. Fluidic actuators require a pressure source, which limits their mobility and mainstream usage. This paper considers instances of mechanisms made from distributed elastomer actuators to generate motion using a chemical means of pressure generation. A mechanical feedback loop controls the chemical decomposition of hydrogen peroxide into oxygen gas in a closed container to self-regulate the actuation pressure. This on-demand pressure generator, called the pneumatic battery, bypasses the need for electrical energy by the direct conversion of chemical to mechanical energy. The portable pump can be operated in any orientation and is used to supply pressure to an elastomeric rolling mobile robot as a representative for a family of soft robots.

Soft Autonomous Materials—Using Active Elasticity and Embedded Distributed Computation

The impressive agility of living systems seems to stem from modular sensing, actuation and communication capabilities, as well as intelligence embedded in the mechanics in the form of active compliance. As a step towards bridging the gap between man-made machines and their biological counterparts, we developed a class of soft mechanisms that can undergo shape change and locomotion under pneumatic actuation. Sensing, computation, communication and actuation are embedded in the material leading to an amorphous, soft material. Soft mechanisms are harder to control than stiff mechanisms as their kinematics are difficult to model and their degrees of freedom are large. Here we show instances of such mechanisms made from identical cellular elements and demonstrate shape changing, and autonomous, sensor-based locomotion using distributed control. We show that the flexible system is accurately modeled by an equivalent spring-mass model and that shape change of each element is linear with applied pressure. We also derive a distributed feedback control law that lets a belt-shaped robot made of flexible elements locomote and climb up inclinations. These mechanisms and algorithms may provide a basis for creating a new generation of biomimetic soft robots that can negotiate openings and manipulate objects with an unprecedented level of compliance and robustness.

Origami-Inspired Printed Robots

Robot manufacturing is currently highly specialized, time consuming, and expensive, limiting accessibility and customization. Existing rapid prototyping techniques (e.g., 3-D printing) can achieve complex geometries and are becoming increasingly accessible; however, they are limited to one or two materials and cannot seamlessly integrate active components. We propose an alternative approach called printable robots that takes advantage of available planar fabrication methods to create integrated electromechanical laminates that are subsequently folded into functional 3-D machines employing origami-inspired techniques. We designed, fabricated, and tested prototype origami robots to address the canonical robotics challenges of mobility and manipulation, and subsequently combined these designs to generate a new, multifunctional machine. The speed of the design and manufacturing process as well as the ease of composing designs create a new paradigm in robotic development, which has the promise to democratize access to customized robots for industrial, home, and educational use.

Visual Servoing-Based Autonomous 2-D Manipulation of Microparticles Using a Nanoprobe

In this paper, autonomous 2-D manipulation and pattern formation of microparticles under an optical microscope by pushing and pulling them with a sharp nanoprobe is presented. For calibration of the camera and to achieve a larger bandwidth on position control, an iterative sliding mode parameter observer is designed that satisfies the Lyapunov stability criterion. A procedure that allows particles to stick near the tip of the nanoprobe while pushing/pulling and to release them when placed to the target position is used for manipulation. For pattern formation, a trajectory planning algorithm based on a metric that defines the blockage of trajectories by particles and target positions is used to order manipulation of particles such that the particle that blocks the most number of trajectories is pulled/pushed to the target position that blocks the least number of trajectories. This ordering of manipulation performs better than the conventional distance-based approaches due to the fact that it minimizes the number of blockages to the linear trajectories. Efficiency of the approach is demonstrated on simulation and experimental results by positioning 4.5-mum diameter polystyrene particles on a flat glass substrate autonomously. The average accuracy of the pushing/pulling operations is less than 0.64 mum.