Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology最新文献

The targeted placement of selected carbon nanotubes is associated with low throughput rates. Hence, this paper presents a novel stage design for the fully automatic assembly of carbon nanotube field-effect transistors (CNTFETs) via mechanical dry transfer. It constitutes the core module of an assembly machine for the precise deployment of nanotubes onto a prefabricated wafer. The mechanical dry transfer approach allows high level of carbon nanotube selectivity with the aim of enabling a high-volume fabrication of ultra-clean devices. The previous production rate of such ultra-clean devices is less than one per hour, which offers a high potential for improvement. The stage consists of a parallel kinematic mechanism (PKM) with 3 degrees of freedom ($X_2{Y}_2{C}_1$) carrying two additional stacked axes ($Z_1{C}_2$). The PKM is suspended on a vacuum preloaded aerostatic bearing, voice coil motors (VCM) and flexure hinges. Together with a combination of high precision and resolution touch probe measurement systems close to its tool center point (TCP), high accuracy and low settling time can be achieved. Based on realistic manufacturing tolerances, a sensitivity analysis of the mechanism’s pseudo rigid body model (PRBM) suggests a theoretical closed-loop error below $0.15\mu m$ over the entire XY workspace of $20\mathrm{mm}\times 2.8\mathrm{mm}$. Measurements of positioning motions show that the settling time can be decreased by the compensation of friction resistances inside the internal bearings of the VCMs.

For inherently compensated aerostatic bearings, the traditional modeling method of describing an air supply orifice with a nodal point results in computational errors when numerical discretization methods, such as the finite difference method, are used particularly for a small air-film thickness. To address this problem, this paper proposes an equivalent pressure-equalizing chamber model (EPECM) to consider the pressure depression around the orifice. First, numerical simulations of the circular centrally fed aerostatic thrust bearing (CCFATB) were conducted using computational fluid dynamics. The discharge coefficient and the radius of the pressure-depression region under various operation conditions were obtained. Subsequently, by combining these two key parameters, the EPECM was applied to analyze the static performances of the CCFATB and annular aerostatic thrust bearing (AATB). The air domain of the AATB was divided into non-uniform grids. The five-point difference scheme and nine-point difference scheme were adopted to solve the Reynolds equation respectively, and the computational results were compared. The proposed model and discretization method were verified by comparing the results with experimental and published data. It is found that the EPECM has a high computational accuracy and superior numerical iteration efficiency compared with the commonly used point-source assumption. The five-point difference scheme is able to deal with the non-uniform mesh model accurately. Moreover, the modified discharge coefficient and pressure-depression region radius calculated in this study provide useful data for performance analysis of inherently compensated air bearings.

Piezoelectric-driven flexure-based multi-DOF motion stages have been widely employed for nano-positioning applications, in which motion-decoupled stages have been extensively investigated in order to facilitate their motion control efforts. Asymmetric motion-decoupled stage designs are simple in configurations and structures, but would cause parasitic shifts of the moving platform. Fully-symmetric motion-decoupled stage designs can minimize parasitic shifts, but would result in complicated configurations and structures. To tackle such difficulties, a new flexure-based motion-decoupled XYZ stage with a quasi-symmetric 3-Prismatic-Prismatic-Prismatic (3-PPP) configuration is proposed in this work. By adding short flexure-based auxiliary supports to the moving platform, a compact quasi-symmetric stage design is achieved, and the parasitic shifts of the moving platform are significantly reduced. To study the kinetostatic performance of the demonstrated embodiment, an analytic stiffness model is formulated and validated by the FEA method. To achieve minimal parasitic shifts, a stiffness matching approach is proposed for the design optimization of structural parameters. A research prototype of the quasi-symmetric stage is fabricated for experimental validation. Experimental results show that the stage achieves workspace of 43.6 μm × 40.3 μm × 63.2 μm, motion resolution of 25 nm, and parasitic shifts of less than 0.94 %, which indicates that the proposed quasi-symmetric design method is effective to reduce the parasitic shifts of the flexure-based nano-positioning stages.

Tracking errors are caused by the amplitude attenuation and phase lag of the servo system to the command. Based on the mechanism, this study proposes the method of command correction which magnifies the amplitude and advances the phase of the command according to the amplitude attenuation and phase lag of the servo system. Firstly, the command is decomposed into stable components and unstable components using Fourier series fitting and Hilbert-Huang transform. Then, the frequency-domain characteristics of the servo system are used to calculate the amplitude attenuation and phase lag of each component. Finally, the stable components and unstable components of the command are corrected by amplifying the amplitude and advancing the phase to compensate for the attenuation and lag caused by the servo system. The experimental results show that the corrected command reduced the average tracking error of the X-axis of the butterfly-shaped trajectory by 66.58 % and the maximum tracking error by 72.28 %. Moreover, the contour error of the butterfly-shaped trajectory was reduced significantly. The proposed method is suitable for the tracking errors and contour error controlling of a trajectory with a drastic curvature change.

The tortuous randomized pores inside porous bronze bring significant challenges to the machining technology and surface morphology evaluation. Additionally, some of the current measurement methods for morphology characterization can only reflect partial information about the porous surface. In this study, the cutting experiments with monocrystal diamond (MCD) tools were conducted on porous bronze to investigate the effects of machining parameters on surface morphology. Moreover, a series of image processing techniques were applied to batch-collected surface images. On this basis, before and after cutting experiments, the fractal dimensions and pore parameters were calculated to characterize and compare the changes in porous surface morphology. The experimental results indicated that the increase in cutting depth led to a larger fractal value while increased cutting speeds reduced the complexity of the machined surfaces. Among them, the cutting depth had the greatest influence on the material removal process, when the cutting depth exceeded 20 μm, the material removal process transitioned from the initial single plastic removal mode to the occurrence of brittle spalling. During the plastic removal model, the fractal dimension decreased by a maximum of 6.70 %. However, in the experimental group with brittle spalling, that value increased by 6.28 %. After processing experiments, the surface porosity of all samples ranged from 3.33 % to 12.8 %, showing a change of - 40 % to +52 % compared to the initial surface. Moreover, in this study, the fractal dimensions could provide a more comprehensive evaluation method for porous surface morphology through statistical analysis. The cutting experiments and surface morphology analysis are available to obtain the optimal machining parameters for achieving the relatively desired surface morphology.

This article introduces a novel highly integrated direct drive rotation wire frame mechanism for multi-axis micro wire electrical discharge machine tool. The design allows the micro electrode wire center to rotate along the motor's output shaft by ±90°, enabling machining over a complete circular area. This enhances the rotation precision and reduces the displacement of each axis, ensuring that the length of the electrode wire remains unchanged during the rotation process and thereby maintaining a stable friction force with the V-grooves. Building upon the direct drive rotation wire frame, a six-axis micro-wire electrode discharge machining machine has been developed, facilitating multi-axis coordinated processing. This study establishes the forward and inverse kinematic models using homogeneous transformation matrices to describe each axis's motion of the machine tool. A closed-form solution for the inverse kinematic model has been derived and effectively utilized for machining path planning for the electrode wire. To comprehensively characterize the machine tool's performances, a method that combines coordinate transformation, analytical geometry, and the Monte Carlo approach has been employed to determine the actual working space and the dexterity of the machine tool. Finally, a preliminary experiment with the six-axis micro wire electrical discharge machine tool demonstrates the effectiveness of the proposed direct drive rotation wire frame, verifying the inverse kinematic closed-form solutions, the practical workspace of the machine tool, and the effectiveness of dexterity and geometric error modeling.

Since 1968, as the demand for the broaching process has grown along with the availability of new materials, scientists and engineers have taken a keen interest in exploring the process's many scientific and technical challenges. In the last 56 years, people have been committed to solve the existing difficulties, mainly including the high stiffness and lightweight structure design of broaching machine, broaching technology of complex contour and fir-tree slot of difficult-to-machine materials for engines, green manufacturing technologies, workpiece surface monitoring in broaching processes, tool condition monitoring and life prediction, and so on. In this review, we focus specifically on the comprehensive development of broaching processes and equipment design over the past 56 years. We first review the basic principles of broaching and analyze the breakthrough progress in various research directions in broaching. In addition, we provide a detailed overview and discussion of broaching by keywords, year, country, journal, author and citation using bibliometric analysis for the first time. It is found that faced with the challenges in the field of broaching, researchers remain enthusiastic and have made significant contributions in areas such as process monitoring, equipment design, traditional broaching studies, and green manufacturing. It also gives new insights on the future development direction of broaching machine tools, i.e., in terms of future broaching high precision, intelligence, high efficiency and sustainability. We advocate for a deeper exploration of the broaching process and machine tool technology through extensive research, aiming to create expanded opportunities for scholars and engineers in this field.

The precise thermal error prediction of spindle-bearing systems (SBSs) necessitates a comprehensive analysis of information gathered from multi-source sensors. However, limited data availability due to structural constraints poses challenges to fully characterize the system state. In this study, we introduce a data-model hybrid-driven framework based on sensor optimization placement for accurate thermal error prediction of SBSs. Firstly, a thermal hypernetwork method is developed to consider uneven temperature distribution and establish a unified information fusion model for state estimation. Secondly, based on an analysis of the rapidity and robustness, robust geodesic distance-based fuzzy c-medoid clustering with a simulated annealing algorithm (RGDFCMSA) is proposed to optimize sensor placement by minimizing the information entropy of the system. Next, uncertain parameters with estimability are selected based on SIAN and Sobol’s sensitivity indicator under optimal sensor placement. Furthermore, a multilayer particle filter (MLPF) is proposed to estimate temperature fields and predict the thermal error of SBSs by fusing information from multiple sources with different fidelity. Finally, experiments under different working conditions are conducted to validate the effectiveness and accuracy of the proposed method. The result indicates that the proposed framework is capable of an accurate estimation of the global temperature field, uncertain thermal parameters and thermal errors.

Bulk metallic glasses (BMGs) have excellent mechanical properties, however, it is still challenging to process high-qualtiy BMG structures for their widespread engineering applications. In this work, electrochemical machining (ECM) is adopted to process various small BMG structures with high geometrical precision and surface quality. Firstly, the electrochemical dissolution behavior of a Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ (at.%) BMG in NaNO₃, H₃PO₄, NaCl, and HCl solutions was investigated and discussed. The results shown that obvious corrosion occurred in HCl and NaCl solutions, while mass by-products and pitting corrosion on the workpiece surface in NaCl solution affect the corrosion continuity and surface quality. Therefore, the HCl solution is selected as the electrolyte for the following ECM process. Secondly, the effects of machining parameters on the ECM performance of BMG workpieces were investigated, where the optimal machining performance was achieved with an electrolyte of 0.1 mol/L HCl, a cathode feed rate of 3 μm/s, a machining voltage of 10 V, and a duty cycle of 15%. Finally, a small round hole with a roughness (Ra) of about 0.2 μm, a sidewall taper of less than 2.83°, and a relative error of diameters of 2.1% was obtained. Another square structure (0.899 mm × 0.891 mm) with high geometrical precision and surface quality was also achieved by the optimal parameters, which validates the feasibility to machine small BMG structures using the ECM technique with its optimal parameters.

¹ In the milling process, due to machining materials and process parameters, the material at the edge of the part may break due to shear forces instead of cutting properly, resulting in the irregular pit (defect) at the exit edge. This seriously affects the surface quality of the workpiece. It is vital to understand the forming mechanism of the exit edge defect (EED) before one tries to eliminate or reduce the size of the EED and furthermore to improve the machining accuracy. Therefore, focusing on the milling process at exit edge of a workpiece, this paper presents a novel theoretical model to study the forming principle of the EED and predict the corresponding size. First, the forming process of the EED is separated into two stages. The beginnings of them are symbolized by the initial- and the fracture-negative shear planes. Then, the initial-negative shear plane which is defined by the initial negative shear angle is found. Furthermore, the location of the fracture-negative shear plane is defined using the fracture negative shear angle to study the EED. For the next step, the concentration force of Flamant-Boussinesq problem combined with the yield strength of the material is introduced to obtain the initial negative shear angle. Additionally, using the energy conservation theory, the negative fracture shear angle is calculated. Based on these, the mechanism of the EED is illustrated. Besides, the size (including length and depth) of the EED is predicted based on the geometric relationship between the initial and the fracture negative shear angle. Finally, the correctness of the theoretical model is verified by simulation and experiments. This study provides a promising step to reducing/eliminating the hazards of edge defects.