Shape dominantly determines function. The performance of engineering products heavily depends on their shapes. Since CAD technology has advanced enough, we can create digital models of complex shapes. To manufacture products, the goal of digital engineering is not just to generate and visualize the shapes, but also to perform other value adding activities, i.e., scientific analysis, rapid prototyping, finished parts making and simulation. Sometimes the nature of the shape (self-similarity), the origin of the shape (shapes found in living organisms), the appearances of the shape (aesthetic value), and the nature of the underlying materials (softness, porosity) challenge the modeling building processes. At the same time, the constraints of other systems (e.g., CAE, CAM, Additive Manufacturing Systems [e.g., 3D Printer] and Virtual Reality Systems) dictate what must be done while creating the digital models so that the models do not make any problems in the downstream.

In this special issue fifteen technical papers propose solutions and strategies to various problems related to digital engineering. Some of them deal with CAD and its philosophical background. Others describe methods to register and reconstruct complex shapes from point clouds in the macroscopic and microscopic spaces. Simulation to identify mechanical and electrical properties are discussed in several papers. The shape of grain texture is very complicated and two papers challenge how to generate it on products’ surfaces. Additive manufacturing is very promising and two papers propose new fabrication methods for complex shapes based on it.

The editors deeply appreciate all the authors and anonymous reviewers for their excellent work to make this special issue very unique. We hope that further researches on digital engineering for complex shapes initiated by this special issue will advance our society as well as digital engineering in the future.

This study addresses the integration of Computer-Aided Design (CAD), Theory of Inventive Problem Solving (TRIZ), and Customer Needs for the sake of product development. TRIZ can generate plausible product alternatives, while CAD can produce the digital data for those alternatives. Thus, the TRIZ-CAD outcomes can be organized to produce a questionnaire. When the questionnaire is disclosed to potential customers (respondents), the individual preferences of the respondents can be obtained. However, aggregating the diverse preferences of all respondents and making decisive conclusions based on these is difficult. In this study, we introduce statements regarding the nine fundamental human needs (subsistence, protection, affection, understanding, participation, leisure, creation, identity, and freedom) and TRIZ-CAD outcomes in a questionnaire. As the respondent is human, the product exemplified by the TRIZ-CAD outcomes should fulfill one or more of the fundamental human need. Responses regarding statements of the nine fundamental human needs can be used to aggregate the diverse opinions of all respondents and thereby make a decisive conclusion. We have shown the effectiveness of the abovementioned approach by using a product development case in which the problem is the determination of a car’s external shape. Field data is discussed showing the applicability of the proposed approach.

This paper presents a study developing a model of the ontology of an apparel product and the design thereof. Here, “ontology” means the concepts and relationships between them for apparel and apparel design; ontology models are also called conceptual models. To the best of our knowledge, such a model has not yet been made in the literature of apparel and apparel design. A conceptual model is a foundation for (1) effective human-human communication and collaboration, (2) facilitating the communication among different computer programs for computer-aided design (CAD) of apparel products, and (3) facilitating human-computer interactions necessary to design an apparel product. The conceptual model developed completely captures the semantics of apparel and design, including the 2D pattern and 3D apparel product. An example is presented, providing an impression of the usefulness of this model.

Good ergonomic design is a very important parameter for any product. When designing a human control product, the ergonomics factors should be satisfied to make a product that will not harm the user. Considering that ergonomic factors in the design process are important, this paper presents a design methodology for developing ergonomic products. The ultimate goal of this research is to design and produce a new type of a park bench. A survey has been conducted based on Quality Function Deployment. A 3D-CAD model of the desired park bench was developed from the concept, and various human factor aspects were evaluated in Siemens Jack Ergonomics Software with digital manikins representing anthropometric data to justify the design for users.

We proposed a registration method for aligning short-range point-clouds captured using a portable laser scanner (PLS) to a large-scale point-cloud captured using a terrestrial laser scanner (TLS). As a PLS covers a very limited region, it often fails to provide sufficient features for registration. In our method, the system analyzes large-scale point-clouds captured using a TLS and indicates candidate regions to be measured using a PLS. When the user measures a suggested region, the system aligns the captured short-range point-cloud to the large-scale point-cloud. Our experiments show that the registration method can adequately align point-clouds captured using a TLS and a PLS.

In this paper, we propose a digital shape reconstruction method for micro-sized 3D (three-dimensional) objects based on the shape from silhouette (SFS) method that reconstructs the shape of a 3D model from silhouette images taken from multiple viewpoints. In the proposed method, images used in the SFS method are depth images acquired with a light-field microscope by digital refocusing (DR) of a stacked image along the axial direction. The DR can generate refocused images from an acquired image by an inverse ray tracing technique using a microlens array. Therefore, this technique provides fast image stacking with different focal planes. Our proposed method can reconstruct micro-sized object models including edges, convex shapes, and concave shapes on the surface of an object such as micro-sized defects so that damaged structures in the objects can be visualized. Firstly, we introduce the SFS method and the light-field microscope for 3D shape reconstruction that is required in the field of micro-sized manufacturing. Secondly, we show the developed experimental equipment for microscopic image acquisition. Depth calibration using a USAF1951 test target is carried out to convert relative value into actual length. Then 3D modeling techniques including image processing are implemented for digital shape reconstruction. Finally, 3D shape reconstruction results of micro-sized machining tools are shown and discussed.

Ceramic matrix composite (CMC) is a material with high thermostability. Since it is lower in weight than metals realizing the same thermostability, it has been attracting increasing attention in many fields. It has an inner fabric structure made of ceramics (SiC), and the yarns of the fabric give this material rather high stiffness in the directions the yarns run. To guarantee the stiffness of the material, it is necessary to inspect the yarns. X-ray CT scanning, a non-destructive inspection technique, is one of the best ways to do this. However, the quality of a CT volume of SiC fabric tends to be very low, and the resolution is generally also low because of the restriction on the time given for the inspection and the relatively large size of CMC parts. This paper presents an algorithm for computing the directions of the yarns in an SiC fabric from a low quality CT volume, and it proposes a way to visualize the computed directions for a better recognition of the directions. It also presents some experimental results that show the effects of the proposed algorithms.

For a structural analysis using the finite element method, a hexahedral element is preferable to a tetrahedral element from the viewpoint of accuracy. However, it is very difficult to subdivide a mesh consisting of hexahedral elements if the shape of the mesh is complicated. Hence, in this paper, as a preliminary research, we use a label-driven subdivision method for a two-dimensional mesh, and show that meshes subdivided nonuniformly can guarantee as much accuracy as meshes with uniform subdivision.

The performance of semiconductor devices has improved on introducing increasing refinements to the structures of these devices. This has created various problems at the atomic level. In particular, the presence of dislocations, a type of crystallographic defect, within semiconductor devices poses a major problem. Dislocations accumulated within the device obstruct the movement of electrons and adversely affect the electrical characteristics of the device. However, previous investigations have not sufficiently clarified the relationship between accumulated dislocations and the electrical characteristics of a semiconductor. In this study, we focus on dislocations produced in the fabrication of an impurity-doped ultra-large-scale integration (ULSI) device and, based on a crystal plasticity analysis, perform a simulation of the accumulation of dislocations within the device during the cooling process. We establish an analytical system by which the obtained information on dislocations is applied to a device simulator, in order to evaluate the electrical characteristics by considering the accumulation of dislocations. We investigate the effects that dislocation density and density distribution have on the characteristic current-voltage curve of the device.

This paper proposes an algorithm to compress CAD models in a grid-based Z-map representation while keeping the compression artifacts within a specified value (the maximum difference allowed by the user). A wavelet transform is used for decomposing the input shape into lower and higher frequency patterns. A significant reduction in the data size can be achieved by deleting higher frequency components. We employ a tree structure called the error range (ER) tree to manage error occurrences and determine where to prune branches without increasing the resulting errors in the data compression. The widely used reversible compression method, gzip, is then used to obtain the final compressed model data output. We conducted a series of experiments with 12 sample shape models on a 512 × 512 grid. With a maximum error of 10 μm (a typical value specified for NC milling), the proposed method reduces the data by 90.9% on average and the computational cost of 19 ms is extremely low. The proposed method can be extended to larger CAD models in real applications.

The automated production of products using digital data has been realized in recent years through the development of manufacturing machines. Digital data are also used for automatic texturing. In a product texturing system using digital data, texture information needs to be incorporated in the generation of digital data. However, it is difficult to generate such data manually since it is not easy to fit the texture to the product or to prevent the texture pattern from being stretched or shortened. Therefore, what is needed is a method of automatically generating digital data that yields a seamless texture with little distortion and a method of fitting the texture to the product shape. In this paper, the application of the Angle Based Flattening (ABF) method by Sheffer and de Sturler to the generation of digital data of textures is proposed. Another method to extend the ABF technic to make it more suitable to geometric textures is also proposed.

This study aims to generate grain forms on 3D models by applying Free Form Deformation (t-FFD). As the fully automated placement of grain patterns on curved surfaces tends to generate distorted grain patterns, we propose a method of semi-automatically placing grain patterns, based on simple inputs from the user, as well as of controlling the heights of grain patterns in real sizes in reference to the model sizes. The proposed method has proved to successful in placing the desired grain forms.

Fractal geometry can create virtual models of complex shapes as CAD data, and from these additive manufacturing can directly create physical models. The virtual-model-building capacity of fractal geometry and the physical-model-building capacity of additive manufacturing can be integrated to deal with the design and manufacturing of complex shapes. This study deals with the manufacture of fractal shapes using commercially available additive manufacturing facilities and 3D CAD packages. Particular interest is paid to building physical models of an IFS-created fractal after remodeling it for manufacturing. This article introduces three remodeling methodologies based on binary-grid, convex/concave-hull, and line-model techniques. The measurements of the manufactured fractal shapes are also reported, and the degree of accuracy that can be achieved by the currently available technology is shown.

Stiffness is an important property of mechanical structures, particularly when it is necessary for a structure to contact other structures while in motion. In this study, we employed the advantages of additive manufacturing (AM) technology to create a multi-material structure and to investigate its stiffness properties. Herein, we also present an analytical model for designing a mechanical structure consisting of two-material, single-beam units, which was verified using a finite element simulation in our study. As an example, a two-material structure with the desired stiffness was fabricated using commercially available AM technology and employing both a soft material (natural rubber) and a hard material (acrylonitrile-butadiene-styrene resin, ABS).

It is important to establish new approaches to create value-added products, such as craftwork or artistic goods, that are different from traditional methods of realizing high-quality and low-cost products. Such a production technology is commonly called “dexterous machining.” This study addresses the creation of artistic products by using soft materials with complicated shapes by employing an aqueous solution of sodium acetate to fix a workpiece and to suppress the deformation. Experimental results show that the use of an aqueous solution of sodium acetate has the potential to realize the “dexterous machining” of soft objects.

This paper presents game information analysis by utilizing a digital scorebook system, as the first tool for curling informatics, which supports coaches and players in realizing smart tactics and strategies in the sport of curling. Our research project, called “Curling Informatics,” aims to develop an environment to support curling strategies and tactics by realizing methods to record game information, perform analysis, and provide visualization and sharing of the information.

We found a significant correlation between the differences in shot accuracies and scores from game information collected by our digital scorebook system for more than 200 games played by the Japanese national class. The results suggest that the difference in shot accuracies is related to the difference in game scores. This is valuable new knowledge to support strategic/tactical planning in curling games. However, the correlation for games involving world-class teams becomes weaker than for the Japanese national class because there is scarcely any difference in shot accuracies.

Five-axis machines and multi-tasking machines are widely used because they facilitate integration of work processes and simplification of jigs and set-ups. Along with effective machine use, development of optimum machining such as research on tools and cutting methods to achieve high-speed cutting and increase of material removal rate is being investigated. While these efforts have greatly contributed to furthering of automation and cost reduction at the manufacturing site, complex machine motions and increased demanding work processes can lead to unexpected collisions and tool breakages. To prevent tool breakage caused by unexpected overloading or to improve the inefficient feed rate on the basis of safety considerations, simulations based on numerical control (NC) data are usually performed in advance to evaluate the cutting force. In high-speed, high-efficiency machining, however, the machine does not always execute movements as instructed by the NC data and the predicted cutting force does not always agree with the actual cutting forces. In this study, therefore, we developed an off-line system in which the motion information of each axis of an actual machine is acquired from a computer numerical control (CNC) controller, and is then used to predict the cutting force. The effects of using the proposed method are described in this article.

A new approach for set point generation in the field of 5-axis machining using quasi-redundant degrees of freedom is introduced in this study. In machine tools that possess both rotational and translational axes, no bijective correlation exists between the tool center point and the movement of the machine tool axes based on the manufacturing tolerances. Depending on the manufacturing process, as many as two additional degrees of freedom exist that allow the machine tool axes movement to be optimised within the given manufacturing tolerances with respect to the axes’ inertia. In this study to reduce the mechanical excitation of the machine tool, the jerk of the machine tool axes is minimised. To enhance robustness, the optimisation problem is formulated as a quadratic program with linear constraints. This problem can be solved by using an interior point method. An application example shows that when exploiting quasi-redundancy, the mechanical excitation of the machine tool can be reduced.

A novel approach to geometry optimisation in the field of 2D cutting is presented in this paper. Set point generation inside of state of the art CNCs is divided in the preparation of the geometry and the feed rate generation. The feed rate generation is influenced by parametric derivatives of the given geometry. Due to this fact, the shaping of a B-Spline is carried out by optimisation of the weighted sum of parametric derivatives while the given manufacturing tolerances are maintained. For the sake of robustness, the arising optimisation problem is formulated as a quadratic program with linear constraints, one which can be solved with great efficiency by using an interior point method. In contrast to state of the art methods, the discrete formulation of the problem allows for a pointwise specification of the manufacturing tolerance. Depending on the manufacturing process, the given manufacturing tolerance is shared by different axes, which is shown for a 2D cutting geometry. An application example shows that the geometry optimisation leads to an increase in machining productivity over state of the art methods.

A novel characteristic model-based discrete sliding mode control (CMDSMC) for time delay system is presented in this paper. Firstly, to solve the challenge of establishing a accurate and simple model for time delay system, characteristic theory is applied to establish characteristic mode with time delay. Secondly, due to the uncertainties of time delay system, discrete sliding mode control based on characteristic model is proposed and stability analysis is done. At last, two illustrative examples taken from literatures are included to indicate the simplicity and superiority of the proposed method.