Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

"A picture is worth one thousand words". This proverb comes from Confucius a Chinese philosopher before about 2500 years ago. Now, the essence of these words is universally understood. A picture can be magical in its ability to quickly communicate a complex story or a set of ideas that can be recalled by the viewer later in time. Visual information plays an important role in our society, it will play an increasingly pervasive role in our lives, and there will be a growing need to have these sources processed further. The pictures or images are used in many application areas like architectural and engineering design, fashion, journalism, advertising, entertainment, etc. Thus it provides the necessary opportunity for us to use the abundance of images. However, the knowledge will be useless if one can't _nd it. In the face of the substantive and increasing apace images, how to search and to retrieve the images that we interested with facility is a fatal problem: it brings a necessity for image retrieval systems. As we know, visual features of the images provide a description of their content. Content-based image retrieval (CBIR), emerged as a promising mean for retrieving images and browsing large images databases. CBIR has been a topic of intensive research in recent years. It is the process of retrieving images from a collection based on automatically extracted features.

/pdf/a-survey-of-shape-feature-extraction-techniques-3qmkhziio7.pdf

A Survey of Shape Feature Extraction Techniques

Reconfigurable antennas change polarization, operating frequency, or far-field pattern in order to cope with changing system parameters. This paper reviews some of the past and current technology applicable to reconfigurable antennas, with several examples of implementations. Mechanically movable parts and arrays are discussed, as well as more-recent semiconductor-component and tunable-material technologies applicable to reconfigurable antennas.

Reconfigurable Antennas

Origami, the ancient art of paper folding, has inspired the design of engineering devices and structures for decades. The underlying principles of origami are very general, which has led to applications ranging from cardboard containers to deployable space structures. More recently, researchers have become interested in the use of active materials (i.e., those that convert various forms of energy into mechanical work) to effect the desired folding behavior. When used in a suitable geometry, active materials allow engineers to create self-folding structures. Such structures are capable of performing folding and/or unfolding operations without being kinematically manipulated by external forces or moments. This is advantageous for many applications including space systems, underwater robotics, small scale devices, and self-assembling systems. This article is a survey and analysis of prior work on active self-folding structures as well as methods and tools available for the design of folding structures in general and self-folding structures in particular. The goal is to provide researchers and practitioners with a systematic view of the state-of-the-art in this important and evolving area. Unifying structural principles for active self-folding structures are identified and used as a basis for a quantitative and qualitative comparison of numerous classes of active materials. Design considerations specific to folded structures are examined, including the issues of crease pattern identification and fold kinematics. Although few tools have been created with active materials in mind, many of them are useful in the overall design process for active self-folding structures. Finally, the article concludes with a discussion of open questions for the field of origami-inspired engineering.

https://iopscience.iop.org/article/10.1088/0964-1726/23/9/094001/pdf

Origami-inspired active structures: a synthesis and review

Various compliant mechanism synthesis methods have been developed over the past decade; however, very little attention has been directed towards adaptive shape change problems. In this paper, we present a systematic method for synthesizing compliant mechanisms to morph a given curve or profile into a target curve utilizing minimum number of actuators (typically one). Two objective functions are formulated, using Least Square Errors and a modified Fourier Transformation, to capture the shape differences. The topology and dimensions of the optimal compliant mechanism are generated using Genetic Algorithms. Applications of this synthesis approach are demonstrated through two adaptive antenna design examples.

Design of Compliant Mechanisms for Morphing Structural Shapes

This paper introduces the benefits of exploiting elasticity in the engineering design of surgical tools, in general, and of minimally invasive procedures, in particular. Compliant mechanisms are jointless mechanisms that rely on elastic deformation to transmit forces and motion. The lack of traditional joints in these single-piece flexible structures offers many benefits, including the absence of wear debris, pinch points, crevices, and lubrication. Such systems are particularly amenable to embedded sensing for haptic feedback and embedded actuation with active-material actuators. The paper provides an overview of design synthesis methods developed at the Compliant Systems Design Laboratory and focuses specifically on surgical applications. Compliant systems have potential to integrate. well within the constraints of laparoscopic procedures and telerobotic surgery. A load-path representation is used within a genetic algorithm to solve two gripper example problems. In addition, the paper illustrates the design and construction of an organ (kidney) manipulator for use in minimally invasive procedures.

Design and Application of Compliant Mechanisms for Surgical Tools

A unified approach to topology and dimensional synthesis of compliant mechanisms is presented in this paper as a discrete optimization problem employing both discrete (topology) and continuous (size) variables. The synthesis scheme features a design parameterization method that treats load paths as discrete design variables to represent various topologies, thereby ensuring structural connectivity among the input, output, and ground supports. The load path synthesis approach overcomes certain design issues, such as "gray areas" and disconnected structures, inherent in previous design schemes. Additionally, multiple gradations of structural resolution and a variety of configurations can be generated without increasing the number of design variables. By treating topology synthesis as a discrete optimization problem, the synthesis approach is incorporated in a genetic algorithm to search for feasible topologies for single-input single-output compliant mechanisms. Two design examples, commonly seen in the compliant mechanisms literature, are included to illustrate the synthesis procedure and to benchmark the performance. The results show that the load path synthesis approach can effectively generate well-connected compliant mechanism designs that are free of gray areas.

Topology and dimensional synthesis of compliant mechanisms using discrete optimization

The synthesis of shape morphing compliant mechanism is inherently different from the typical single output design problems, due to the multiple output points along the morphing boundary. We have previously developed a genetic algorithm (GA)-based synthesis approach, incorporating a binary ground structure parameterization, to systematically design shape morphing compliant mechanisms. However, the approach is ineffective due to issues such as the generation of disconnected structures and the need to choose an initial mesh. In this paper, we present the 'load path representation,' which is developed to overcome the issues encountered using the binary ground structure parameterization. The performance of the load path approach over the binary ground structure approach is demonstrated through several design examples. The results have shown that the load path approach offers several advantages, such as (a) eliminating the need of an initial ground structure, (b) ensuring structural connectivity, and (c) yielding solutions that generate desired shape change efficiently.

An effective method of synthesizing compliant adaptive structures using load path representation

Most aircraft wings are optimized to produce minimum drag under one particular flying speed, while the flying speed actually varies continuously throughout flight. Although conventional hinged mechanisms can change the wing shape in response to the change in flying speed, the connecting hinges create discontinuities over the wing surface, leading to earlier airflow separation. In this paper, we propose a systematic approach to synthesize compliant mechanisms that can deform an initial curve into a target shape with a smooth boundary. As opposed to the two-step synthesis that separates the interrelated topology and dimensional aspects of a compliant mechanism, we propose an optimization model using a mixed-variable formulation that addresses both aspects simultaneously. The effectiveness of the shape change is evaluated using Fourier Descriptors (FDs), which capture the pure 'shape' differences between curves. Due to the discrete nature in the design variables, a Genetic Algorithm (GA) is employed to find the optimal solution. The preliminary results demonstrate the feasibility of simultaneously addressing the topology and dimensional aspects. They also indicate that the reference shape used for curve description can significantly affect the optimal solutions. This suggests that a more refined objective function is necessary to improve the effectiveness of the results.

Kerr Jia Lu

Papers

Design of Compliant Mechanisms for Morphing Structural Shapes

Design and Application of Compliant Mechanisms for Surgical Tools

Topology and dimensional synthesis of compliant mechanisms using discrete optimization

An effective method of synthesizing compliant adaptive structures using load path representation

Compliant mechanism synthesis for shape-change applications: preliminary results