J. Mechanisms Robotics. 2015;7(2):020201-020201-2. doi:10.1115/1.4029640.

The past two decades have seen immense strides being made in novel fabrication techniques, particularly in additive manufacturing (AM) technologies, also known as “rapid prototyping” and “3D printing,” as well as in novel subtractive techniques such as laser-cutting and waterjet-cutting. The most popular practical technologies, such as fused-deposition modeling (FDM), stereolithography, selective-laser-sintering, and laser-cutting, are currently used worldwide and are rapidly becoming even more widespread and inexpensive. While all these processes enable rapid and easy fabrication of parts with complex geometries, they are limited in a number of ways, including a small number of available materials, low strength of fabricated parts, and are generally only capable of producing monolithic components.

Commentary by Dr. Valentin Fuster

Research Papers

J. Mechanisms Robotics. 2015;7(2):021001-021001-7. doi:10.1115/1.4029436.

This paper presents a method for fabricating millimeter-scale robotic components for minimally invasive surgery. Photolithographic patterning is used to create a framework of carbon nanotubes (CNTs) that can be infiltrated with a variety of materials, depending on the desired material properties. For the examples shown in this paper, amorphous carbon is used as the infiltration material. The planar frameworks are then stacked to create the 3D device. The detail and precision are affected by large changes in cross section in the direction of stacking. Methods for improving the definition of the 3D object due to changing cross section are discussed. The process is demonstrated in a two-degree-of-freedom (2DOF) wrist mechanism and a 2DOF surgical gripping mechanism, which have the potential of decreasing the size of future minimally invasive surgical instruments.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021002-021002-10. doi:10.1115/1.4029400.

This paper describes a novel fabrication technique called hybrid deposition manufacturing (HDM), which combines additive manufacturing (AM) processes such as fused deposition manufacturing (FDM) with material deposition and embedded components to produce multimaterial parts and systems for robotics, mechatronics, and articulated mechanism applications. AM techniques are used to print both permanent components and sacrificial molds for deposited resins and inserted parts. Design strategies and practical techniques for developing these structures and molds are described, taking into account considerations such as printer resolution, build direction, and printed material strength. The strengths of interfaces between printed and deposited materials commonly used in the authors' implementation of the process are measured to characterize the robustness of the resulting parts. The process is compared to previously documented layered manufacturing methodologies, and the authors present examples of systems produced with the process, including robot fingers, a multimaterial airless tire, and an articulated camera probe. This effort works toward simplifying fabrication and assembly complexity over comparable techniques, leveraging the benefits of AM, and expanding the range of design options for robotic mechanisms.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021003-021003-10. doi:10.1115/1.4029473.

To build multimaterial objects using additive manufacturing (AM), modifications to the majority of current conventional AM processes are required. Typically, deposition can only occur on flat surfaces and motion requires three degrees of freedom (DOFs) in a Cartesian coordinate system. In this work, metal wire and mesh were successfully embedded using ultrasonic energy on curved thermoplastic structures fabricated via the material extrusion AM technology named fused deposition modeling (FDM). The direct wire embedding process was executed by installing an ultrasonic horn on a three-axis prismatic machine and fixing an FDM-built curved part on a rotary stage. Since the part was nonplanar, a need existed to accurately place metal wire along the curved surface with positions defined by Cartesian and angular coordinates. Two additional DOFs were generated by moving both the build platform and tool head, and trajectory planning allowed for synchronized motion between the two motion systems.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021004-021004-10. doi:10.1115/1.4029435.

While techniques exist for the rapid prototyping of mechanical and electrical components separately, this paper describes a method where commercial additive manufacturing (AM) techniques can be used to concurrently construct the mechanical structure and electronic circuits in a robotic or mechatronic system. The technique involves printing hollow channels within 3D printed parts that are then filled with a low melting point liquid metal alloy that solidifies to form electrical traces. This method is compatible with most conventional fused deposition modeling and stereolithography (SLA) machines and requires no modification to an existing printer, though the technique could easily be incorporated into multimaterial machines. Three primary considerations are explored using a commercial fused deposition manufacturing (FDM) process as a testbed: material and manufacturing process parameters, simplified injection fluid mechanics, and automatic part generation using standard printed circuit board (PCB) software tools. Example parts demonstrate the ability to embed circuits into a 3D printed structure and populate the surface with discrete electronic components.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021005-021005-7. doi:10.1115/1.4029492.

Biological systems such as the gecko are complex, involving a wide variety of materials and length scales. Bio-inspired robotic systems seek to emulate this complexity, leading to manufacturing challenges. A new design for a membrane-based gripper for curved surfaces requires the inclusion of microscale features, macroscale structural elements, electrically patterned thin films, and both soft and hard materials. Surface and shape deposition manufacturing (S2DM) is introduced as a process that can create parts with multiple materials, as well as integrated thin films and microtextures. It combines SDM techniques, laser cutting and patterning, and a new texturing technique, surface microsculpting. The process allows for precise registration of sequential additive/subtractive manufacturing steps. S2DM is demonstrated with the manufacture of a gripper that picks up common objects using a gecko-inspired adhesive. The process can be extended to other integrated robotic components that benefit from the integration of textures, thin films, and multiple materials.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021006-021006-11. doi:10.1115/1.4029493.

This paper details the design, analysis, fabrication, and validation of a deployable, atraumatic grasper intended for retraction and manipulation tasks in manual and robotic minimally invasive surgical (MIS) procedures. Fabricated using a combination of shape deposition manufacturing (SDM) and 3D printing, the device (which acts as a deployable end-effector for robotic platforms) has the potential to reduce the risk of intraoperative hemorrhage by providing a soft, compliant interface between delicate tissue structures and the metal laparoscopic forceps and graspers that are currently used to manipulate and retract these structures on an ad hoc basis. This paper introduces a general analytical framework for designing SDM fingers where the desire is to predict the shape and the transmission ratio, and this framework was used to design a multijointed grasper that relies on geometric trapping to manipulate tissue, rather than friction or pinching, to provide a safe, stable, adaptive, and conformable means for manipulation. Passive structural compliance, coupled with active grip force monitoring enabled by embedded pressure sensors, helps to reduce the cognitive load on the surgeon. Initial manipulation tasks in a simulated environment have demonstrated that the device can be deployed though a 15 mm trocar and develop a stable grasp using Intuitive Surgical's daVinci robotic platform to deftly manipulate a tissue analog.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021007-021007-9. doi:10.1115/1.4029497.

This paper details the design and fabrication process of a fully integrated soft humanoid robotic hand with five finger that integrate an embedded shape memory alloy (SMA) actuator and a piezoelectric transducer (PZT) flexure sensor. Several challenges including precise control of the SMA actuator, improving power efficiency, and reducing actuation current and response time have been addressed. First, a Ni-Ti SMA strip is pretrained to a circular shape. Second, it is wrapped with a Ni-Cr resistance wire that is coated with thermally conductive and electrically isolating material. This design significantly reduces actuation current, improves circuit efficiency, and hence reduces response time and increases power efficiency. Third, an antagonistic SMA strip is used to improve the shape recovery rate. Fourth, the SMA actuator, the recovery SMA strip, and a flexure sensor are inserted into a 3D printed mold which is filled with silicon rubber materials. The flexure sensor feeds back the finger shape for precise control. Fifth, a demolding process yields a fully integrated multifunctional soft robotic finger. We also fabricated a hand assembled with five fingers and a palm. We measured its performance and specifications with experiments. We demonstrated its capability of grasping various kinds of regular or irregular objects. The soft robotic hand is very robust and has a large compliance, which makes it ideal for use in an unstructured environment. It is inherently safe to human operators as it can withstand large impacts and unintended contacts without causing any injury to human operators or damage to the environment.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021008-021008-9. doi:10.1115/1.4029474.

Whole-body-contact sensing will be crucial in the quest to make robots capable of safe interaction with humans. This paper describes a novel design and a fabrication method of artificial tactile sensing skin for robots. The manufacturing method described in this paper allows easy filling of a complex microchannel network with a liquid conductor (e.g., room temperature ionic liquid (RTIL)). The proposed sensing skin can detect the magnitude and location of surface contacts using electrical impedance tomography (EIT), an imaging technique mostly used in the medical field and examined recently in conjunction with sensors based on a piezoresistive polymer sheet for robotic applications. Unlike piezoresistive polymers, our IL-filled artificial skin changes its impedance in a more predictable manner, since the measured value is determined by a simple function of the microchannel geometry only, rather than complex physical phenomena. As a proof of concept, we demonstrate that our EIT artificial skin can detect surface contacts and graphically show their magnitudes and locations.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021009-021009-8. doi:10.1115/1.4029491.

Intelligent robotic systems that can react to unprogrammed tasks and unforeseen environmental changes require augmented “softness.” Robogami, a low-profile origami robot, addresses intrinsic (material-wise) and extrinsic (mechanism-wise) softness with its multi-degree-of-freedom (DOF) body driven by soft actuators. The unique hardware of the Robogami and its submillimeter thick construction enable diverse transformations as those achievable by the paper origami. The presented Robogami shows the first fully integrated version that has all the essential components including its controller within a thin sheet. Construction of this robot is possible via precise, repeatable, and low cost planar fabrication methods often reserved for microscale fabrications. In this research, we aim at expanding the capabilities of Robogamis by embedding bidirectional actuation, sensing, and control circuit. To assess the performance of the proposed sensors and actuators, we report on the performance of these components in a single module and in the four-legged crawler robot.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021010-021010-10. doi:10.1115/1.4029489.

A layer-based manufacturing method using composite microstructures is widely used for mesoscale robot fabrication. This fabrication method has enabled the development of a lightweight and robust jumping robot, but there are limitations in relation to the embedding of elastic components. In this paper, a fabrication method for embedding an elastic component at an angled position is developed, extending the capability of the composite microstructures. This method is then used to build an axial spring attached to the bistable mechanism of a jumping robot. Sheet metal is used as an elastic component, which is stamped after the layering and curing process, thereby changing the neutral position of the spring. Two linear springs are designed to be in parallel with a joint to impose bistability; thereby delivering two stable states. This bistable mechanism is triggered with a shape memory alloy (SMA) coil spring actuator. A small-scale jumping mechanism is then fabricated using this mechanism; it jumps when the snap-through of the bistable mechanism occurs. A model of the stamped sheet metal spring is built based on a pseudo rigid body model (PRBM) to estimate the spring performance, and a predictive sheet metal bending model is also built to design the die for stamping. The experimental results show that the stamped sheet metal spring stores 12.63 mJ of elastic energy, and that the mechanism can jump to a height of 175 mm with an initial takeoff velocity of 1.93 m/s.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021011-021011-19. doi:10.1115/1.4029495.

Inspired by the exoskeletons of insects, we have developed a number of manufacturing methods for the fabrication of structures for attachment, protection, and sensing. This manufacturing paradigm is based on infrared laser machining of lamina and the bonding of layered structures. The structures have been integrated with an inexpensive palm-sized legged robot, the VelociRoACH [Haldane et al., 2013, “Animal-Inspired Design and Aerodynamic Stabilization of a Hexapedal Millirobot,” IEEE/RSJ International Conference on Robotics and Automation, Karlsruhe, Germany, May 6–10, pp. 3279–3286]. We also present a methodology to design and fabricate folded robotic mechanisms, and have released an open-source robot, the OpenRoACH, as an example implementation of these techniques. We present new composite materials which enable the fabrication of stronger, larger scale smart composite microstructures (SCM) robots. We demonstrate how thermoforming can be used to manufacture protective structures resistant to water and capable of withstanding terminal velocity falls. A simple way to manufacture traction enhancing claws is demonstrated. An electronics layer can be incorporated into the robot structure, enabling the integration of distributed sensing. We present fabrication methods for binary and analog force sensing arrays, as well as a carbon nanotube (CNT) based strain sensor which can be fabricated in place. The presented manufacturing methods take advantage of low-cost, high accuracy two-dimensional fabrication processes which will enable low-cost mass production of robots integrated with mechanical linkages, an exoskeleton, and body and limb sensing.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021012-021012-13. doi:10.1115/1.4029490.

Print-and-fold manufacturing has the potential to democratize access to robots with robots that are easier to fabricate using materials that are easier to procure. Unfortunately, a lack of understanding about how motion can be achieved by folding hinders the scope of print-and-fold robots. In this paper, we show how the basic joints used in robots can be constructed using print-and-fold. Our patterns are parameterized so that users not only get the desired degrees of freedom but can also specify the joint's range of motion. The joints can be combined with each other to achieve higher degrees of freedom or with rigid bodies to produce foldable linkages. We have folded our basic joints and measured their force–displacement curves. We have composed them into joints with higher degrees of freedom and into foldable mechanisms and found that they achieve the expected kinematics. We have also added actuators and control circuitry to our joints and mechanisms, showing that it is possible to print and fold entire robots with many different kinematics using a uniform process.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021013-021013-8. doi:10.1115/1.4029548.

This paper describes a method for manufacturing complex three-dimensional curved structures by self-folding layered materials. Our main focus is to first show that the material can cope with curved crease self-folding and then to utilize the curvature to predict the folding angles. The self-folding process employs uniform heat to induce self-folding of the material and shows the successful generation of several types of propellers as a proof of concept. We further show the resulting device is functional by demonstrating its levitation in the presence of a magnetic field applied remotely.

Topics: Propellers , Blades , Design
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021014-021014-10. doi:10.1115/1.4029494.

The wormlike robots are capable of imitating amazing locomotion of slim creatures. This paper presents a novel centimeter-scale worm robot inspired by a kirigami parallel structure with helical motion. The motion characteristics of the kirigami structure are unravelled by analyzing the equivalent kinematic model in terms of screw theory. This reveals that the kirigami parallel structure with three degrees-of-freedom (DOF) motion is capable of implementing both peristalsis and inchworm-type motion. In light of the revealed motion characteristics, a segmented worm robot which is able to imitate contracting motion, bending motion of omega shape and twisting motion in nature is proposed by integrating kirigami parallel structures successively. Following the kinematic and static characteristics of the kirigami structure, actuation models are explored by employing the linear shape-memory-alloy (SMA) coil springs and the complete procedure for determining the geometrical parameters of the SMA coil springs. Actuation phases for the actuation model with two SMA springs are enumerated and with four SMA springs are calculated based on the Burnside's lemma. In this paper, a prototype of the worm robot with three segments is presented together with a paper-made body structure and integrated SMA coil springs. This centimeter-scale prototype of the worm robot is lightweight and can be used in confined environments for detection and inspection. The study presents an interesting approach of integrating SMA actuators in kirigami-enabled parallel structures for the development of compliant and miniaturized robots.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(2):021015-021015-10. doi:10.1115/1.4029496.

This work presents a system by which users can easily create printable origami-inspired robots from high-level structural specifications. Starting from a library of basic mechanical, electrical, and software building blocks, users can hierarchically assemble integrated electromechanical components and programmed mechanisms. The system compiles those designs to cogenerate complete fabricable outputs: mechanical drawings suitable for direct manufacture, wiring instructions for electronic devices, and firmware and user interface (UI) software to control the final robot autonomously or from human input. This process allows everyday users to create on-demand custom printable robots for personal use, without the requisite engineering background, design tools, and cycle time typical of the process today. This paper describes the system and its use, demonstrating its abilities and versatility through the design of several disparate robots.

Commentary by Dr. Valentin Fuster

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