With MEMS/NEMS being intensively developed for both consumer and industrial products, micro-nanofabrication is now moving from academics to industrial use. MEMS/NEMS and precision microdevices used in conventional photolithography, technology and suitable fabrication methods are now being selected based on materials, device structure, and fabrication cost, among others. These fabrication methods could become the frontier of manufacturing technology in many application areas.

The themes treated in this special issue include the latest advanced research on micro-nanomaterials and processing for MEMS/NEMS and precision microdevices. These papers are expected to contribute much to further developing MEMS/NEMS and precision microdevices.

In closing, I would like to thank the authors for their valuable submissions and the reviewers for their incisive efforts, without which this special issue would not have been possible. We are most grateful to all who have contributed their time and effort to ensuring this issue’s success.

This paper describes the process of fabricating micro thermoelectric generators (μ-TEGs) based on antimony telluride (Sb-Te) and bismuth telluride (Bi-Te). These materials have excellent thermoelectric (TE) conversion properties. The deposition and patterning processes for thermoelectric films are key techniques in the fabrication of μ-TEGs. However, it is difficult to form TE micropatterns using conventional semiconductor technologies because Sb-Te and Bi-Te are brittle and difficult to etch. Therefore, a semiconductor fabrication process is developed for TE film patterning. Here, various processes for depositing Sb-Te and Bi-Te TE films are described. Then, the combinations of the deposition and patterning techniques are reviewed. Finally, the generation properties of the μ-TEGs are summarized.

The operational error of a virtual reality (VR) assisted vision-based microassembly system is measured and calibrated during the system development stage. The vision-based microassembly system was designed and its opto-mechanical model was established in a virtual environment. By measuring the errors between the representative points in the images of virtual cameras and charge-coupled device (CCD) visual systems, the errors in the virtual environment were compensated by correcting the projection matrix parameters, the view matrix parameters, the initial components position, and the deviation angle for the working stage motion. The effectiveness of the proposed VR-assisted fine calibration method was tested by performing VR calibration on the virtual system.

A new fabrication process of metal nanodot arrays using the thermal dewetting method was developed in this study. This process was comprised of three steps: thin Au film deposition on a quartz glass substrate, groove patterning by direct nanoimprinting, and self-organization of metal nanodot arrays by thermal dewetting. A new idea to utilize a polymer film mold for groove patterning by direct nanoimprinting was examined. The polymer film mold was prepared by hot-embossing groove patterns of a mother mold on a cyclo olefin polymer (COP) film. The mother mold was prepared from a silicon wafer. The polymer film mold was used for direct nanoimprinting on a metal film deposited on a quartz substrate. The experimental results revealed that the COP film mold can effectively form a micro groove pattern on the Au film despite the COP film mold being softer than the Au film. The micro groove on the Au film was also found to be effective in aligning the nanodots in lines. The micro groove patterning using the COP film mold was also confirmed to be useful in controlling the dot size and alignment during the thermal dewetting process.

Over the last decade, developments of fine grained materials and investigations of the effects of grain size on mechanical processing at the micro scale have been reported. There are several papers and reports on the function improvements achieved due to enhanced edge quality. However, it is difficult to identify the studies about the effects of grain size on the processed surface in laser processing because ultrafine grain materials were not supplied in the market. In this study, the effect of grain size on the depth of groove by laser processing is investigated. Microgrooves are produced using a picosecond laser machine. The grooves are observed with a non-contact 3D measuring machine, and the depth and surface conditions are determined. There are obvious differences on the depth between the different grain sizes. Specimens were cut to allow the observation of the phase transformation of grains in the cross section using scanning electron microscope (SEM) and electron back scatter diffraction (EBSD). There are several obstacles when producing deeper grooves. As a result, smaller grained stainless steels are suitable for producing microparts by microlaser cutting.

In technologies involving micro electromechanical systems, lift-off processes combined with sputter deposition are general patterning methods for the formation of amorphous alloy thick film structures. However, the thicknesses of structures fabricated in this manner are not uniform because sputtered particles are blocked by the sidewalls of the lift-off layer. In this paper, a reverse lift-off process is proposed as a new patterning method for fabricating amorphous alloy thick film structures of uniform thickness. In the reverse lift-off process, a template of the desired structure is formed on top of the chosen substrate. The thick film structure is then formed by sputter deposition on the top surface of the template. In contrast to a conventional lift-off process, here the thickness of the structure is uniform because there is nothing to hinder the sputtered particles. To demonstrate this process, we successfully fabricated a Cu-Zr-Ti metallic glass thick film structure with a uniform film thickness and a rectangular cross section across different target structure widths and thicknesses. This demonstrates that the reverse lift-off process is more suitable than conventional lift-off processes for the fabrication of metallic glass thick film structures.

A mosquito’s proboscis, which is used for sucking blood, consists of seven complicated parts. For example, the labrum has a hollow structure, and the maxillae have micrometer-sized tooth like projections on its tip. In this study, microneedles imitating one labium and two maxillae were fabricated using a precision three-dimensional laser lithography system “Nanoscribe.” The maximum length of the fabricated microneedle was 2.0 mm, the minimum length required to reach human capillary blood vessel underneath the epidermis.

In this paper, we investigate the characteristics of Ti-Ni-Zr thin film metallic glasses (TFMGs)/ shape memory alloys (SMAs) for microelectromechanical systems (MEMS) applications with three-dimensional structures. The amorphous Ti-Ni-Zr thin films having a Ni content of more than 50 at.% and Zr content of more than 11 at.% undergo glass transitions and are TFMGs. The Ti₃₉Ni₅₀Zr₁₁ TFMG has the lowest glass transition temperature T_g of 703 K and a wide supercooled liquid region ΔT of 57 K. Moreover, it has high thermal stability at T_g. However, the apparent viscosity of the Ti₃₉Ni₅₀Zr₁₁ is higher than those of other Ti-Ni-Zr TFMGs. Moreover, the Ti-Ni-Zr TFMG exhibits higher viscosity than conventional TFMGs because the alloy composition of Ti-Ni-Zr TFMGs/SMAs is far from the eutectic point.

A laser modification method to control the surface wettability of a silicon and borosilicate glass substrate is proposed and demonstrated. The wettability of the silicon surface decreases after 2.5 W laser irradiation without a change in surface morphology. When the laser power is greater than 4 W, it results in the formation of a 10-nm-deep groove and the wettability increases. These phenomena are caused by changes in the number of surface groups and morphology, respectively. On the other hand, the glass surface is modified by infrared laser irradiation and the treated surface is highly hydrophilic. Surface analysis by FT-IR indicates that the modification is the result of an increase in the number of silanol groups. The proposed modification method is applied to micro-fluidic systems. A modified line can function as a surface micro-channel. Furthermore, with a gradient in wettability, the micro-channel has the ability to self-transport water droplets.

We demonstrate the heat-resistant property of a Ni-W electroformed mold (Ni-W mold) used as the micro imprinting die for an Al alloy. To enhance the transfer performance of the Ni-W mold to A2017, we carried out micro imprinting for A2017 at 600°C. However, entire Ni-W patterns stuck to A2017. It is considered that Al, a major component of A2017, and Ni, a major component of a Ni-W mold, formed an intermetallic compound at 600°C.

Demands for machine tools that are highly accurate, productive, flexible, and compact have been growing in the aerospace, automotive, energy, factory automation, and other industries. Rationally meeting these severe, complex requirements has led to numerous research and development activities involving machine tools. Few machine tool technologies have been established, however, despite the machine tool industry’s long history. Within the next several years, the rapid change and enlargement of the industries will certainly require the realization of innovative machine tools.

This mini special issue on machine tool structure and its design optimization features 8 papers classified under the following themes:

- Enhancing high static and dynamic rigidity

- Minimizing and optimizing thermal deformation

- Proposing new structural analysis methods for machine tools

- Selecting and applying new structural materials to the machine tool structure

- Applying new structural designs and mechanisms

These papers present new design concepts, design methods, and innovative examples in machine tool development. I believe that successfully combining these core technologies will provide machine tool compatible with future manufacturing environments.

In closing, I would like to express my sincere gratitude to the authors and reviewers for their interesting and dedicated contributions to this special issue.

The support stiffness model and the stiffness tuning technique are applied to a practical situation. The support stiffness model is integrated with finite element analysis (FEA) to simulate the rocking vibration mode. The support stiffness of a machining center prototype is calculated based on the support stiffness model. The stiffness tuning technique is used to determine the placement of support structures in the simulation. The calculated support stiffness is integrated into a three dimensional model as springs. Rocking vibration modes are obtained from simulations by using the support stiffness model. To compare the results, a simulation without the support stiffness model is conducted. An experiment is also conducted on the same machining center that is used in the simulation. Without the support stiffness model, the difference between the experimental and simulation natural frequencies was above 19%. In contrast, the difference is under 10% when the support stiffness model is included. The experimental and the simulation results were in good agreement with respect to the rocking vibration modes. These results demonstrate that incorporating the support stiffness model into finite element analysis increases the calculation accuracy of the rocking-vibration-mode natural frequencies. Consequently, the support stiffness model and the stiffness tuning technique are effective for designing the support systems of machine tools.

In this study, we have constructed a mathematical model that can analyze the coupled vibration of machine tool structure and feed drive systems. The model is proposed on the basis of the modal analysis of the actual machine tool structure. It consists of three translational and three rotational displacements of the bed, relative angular deformations between the bed and column, relative translational and angular deformations between the bed and saddle, and relative translational and angular deformations between the column and spindle head. In addition, each feed drive system is modeled using a vibration model, which has two degrees of freedom. The servo controllers of each axis are also modeled. To confirm the validity of the proposed model, frequency responses, motion trajectories of the feedback positions, linear scale positions, and the relative displacement between the table and head are measured and simulated. The effect of coupled vibrations on the tracking errors is examined with the help of both experiments and simulations. To investigate the effect of the servo systems on the vibration, both experiments and simulations are carried out by using feed drive systems in the following three conditions: mechanically clamped, servo-on, and servo-off. The results of experiments and the simulations show that the proposed model can express the mode of vibration and the influence of the condition of feed drive systems on the mode of vibration.

A spindle cooling technology that directly cools the rotating spindle near the front bearing is effective in achieving a high-precision, high-rigidity spindle for a machining center. In conventional spindle cooling technologies, the entire spindle is cooled, which results in high cost and low efficiency. The writer developed a spindle cooling technology in which cooling is concentrated only in the necessary areas, and thus realized a low-cost, highly efficient method of cooling.

In order to improve the productivity and flexibility of the conventional turning machines, multi-tasking turning machines are developed to simultaneously perform several machining operations. In this study, a multi-axis controlled turning machine equipped with a swing-type B-axis turret head is developed that allows multiple turning processes to be performed. In particular, the structural design of the turret head is discussed in detail.

A technology for creating new composite materials with hybrid properties desired by many designers was developed and evaluated. Young’s modulus, density, coefficient of linear expansion, specific heat and thermal conductivity were calculated through a newly developed software. This software has two functions which are (1) the selection of adequate materials and the calculation of their ratios to achieve specific desired properties in a new composite material (2) the calculation of resultant properties given that the component materials and their rations in a composite material are known. The new composite material for the tool post of a machine tool was manufactured and evaluated. It is concluded from the results that the technology was very effective and useful for development of a new composite material with several hybrid properties.

While many components used in automobiles, household electric appliances, etc., are becoming more compact, the size of most machine tools used to work on such components remains unchanged. Therefore, to improve the efficient use of factory space and economical use of energy, machine tools that are comparable in size to workpieces are required. Thus far, we have focused our developmental efforts on the miniaturization of machine tools, e.g., a lathe with a width ten times the machining diameter of a workpiece and a lathe with a bed made of a pipe frame truss structure. Based on these past study results, we have newly developed a desktop machine tool with a pipe frame structure. This paper reports on the developmental background and overview of the developed machine tool, its characteristics, its evaluation results, and our future plans.

Machine tool structures are usually caught in the dichotomies of mass, static rigidity, working area, and dynamic rigidity. This dichotomies are mainly dependent on the mass specific stiffness of the structure material. Fiber reinforced plastics can offer a significantly higher mass specific stiffness than steel can and are therefore able to mollify this dichotomies for machine tool structures. The challenge the machine tool industry faces, though, is the high price of those suitable fiber reinforced plastics, such as carbon fiber reinforced plastics. The price is significantly higher compared to steel components, and it is not clear in which cases or to what extent the simplified equation can generate overall financial benefits. This paper proposes a systematic approach to analyzing criteria and deciding when fiber reinforced plastics can generate added value. Then, a value creation model is derived from the technological performance enhancement that mollified dichotomies can achieve. A simplified example shows how the specific value created by material substitution in a machine component can be extracted using a flexible, multi body method of analysis.

Machine tools and inspection systems require high performance positioning table systems that have long travel ranges, lower profile structures, multi-degree-of-freedom motion, and high speed motion, simultaneously. This paper presents a newly developed low-profile planar motion table system driven by steel belts. The driving system has two steel belts, two servo motors, and four ball spline shafts. These elements are symmetrically arranged on the same plane, and the moving table realizes planar motion. After confirming the effectiveness of the proposed driving mechanism with a one-axis table system, the planar table system developed is evaluated through the some positioning experiments. The results confirm that the developed table system is useful in material handling and other applications.

This paper describes the calculation of the point of contact between assembled parts for remotecontrolled assembly using a haptic device with a single degree of freedom (DOF). To achieve such remote-controlled assembly, it is necessary to judge the constraint state and change the movement direction of the part. It is difficult to detect the points of contact between parts around which the rotational movement should be performed. In this paper, we report a method developed for the purpose of determining the contact point using a six-axis force sensor without knowing the geometry of the parts. The proposed method is applicable to cases in which the theoretical contact point cannot be calculated because of errors and fluctuations in the sensory data. The effectiveness and precision of the method are evaluated through experiments and simulations.

Nowadays, many manufacturers use computer-aided design (CAD) for processes such as computer numerical control (CNC) machining, simulations, and press working. They use CAD models for their simulations because the cost of performance simulations is lower than that of actual product testing. In this paper, we consider hexahedral meshes for finite element analysis because simulations using such meshes are more accurate than those using tetrahedral meshes. Our aim is to automatically generate hexahedral meshes with sharp features that precisely represent the corresponding features of the target shape. Our hexahedral mesh generation algorithm is voxel-based, and thus in our previous studies, we fitted the surface of voxels to the target surface using Laplacian energy minimization. We used normal vectors during the fitting to preserve any existing sharp features. Each face of the boundary surface of a hexahedral mesh is a quadrilateral face, which we consider to consist of four triangles. Herein, we assume that an edge of a quadrilateral surface has four normal vectors of four connected triangles. Here, we diffuse normal vectors of the target shape after extracting them to accurately preserve the shape features. Moreover, for the Laplacian energy, we add a term that matches the normal vector of the target shape with the four normal vectors of a boundary edge. Finally, we present some experimental results using our method.

Application of hybrid robotics is a continuously developing field, as hybrid manipulators have demonstrated that they can combine the benefits of serial structures and parallel mechanisms. In this paper, a novel 5-degree-of-freedom hybrid manipulator is designed. The structure of this manipulator and its kinematics analysis are presented. An innovative closed-form solution was proposed to address the inverse kinematics problem. Additionally, the validity of the closed-form solution was verified via co-simulation using MATLAB and ADAMS. Finally, the reachable workspace of this manipulator was obtained for further optimizing the structure and motion control.

In recent times, numerical simulation techniques have been commonly used to estimate and predict machining parameters such as cutting forces, stresses, and temperature distribution. However, it is very difficult to estimate the flow stress of a workpiece and the friction characteristics at a tool/chip interface, particularly during a high-speed cutting process. The objective of this study is to improve the accuracy of the present method and simultaneously determine the characteristics of the flow stress of a workpiece and friction at the cutting edge under a high strain rate and temperature during the cutting process. In this study, the Johnson-Cook (JC) flow stress model is used as a function of strain, strain rate, and temperature. The friction characteristic was estimated by minimizing the difference between the predicted and measured results of principal force, thrust force, and shear angle. The shear friction equation was used to estimate the friction characteristics. Therefore, by comparing the measured values of the cutting forces with the predicted results from FEM simulations, an expression for workpiece flow stress and friction characteristics at the cutting edge during a high-speed cutting process was estimated.