Measurement technology in the field of production engineering has long played an essential role in improving the yield and reliability of manufactured products, and it will continue to increase in importance to the manufacture of advanced products. The development of intelligent and innovative measurement technologies will not only be essential but also indispensable to the creation of high value-added products as next-generation advanced products, manufactured based on leading-edge production technologies and science. The importance of measurement technologies indispensable to the digitization of things has been increasing particularly dramatically in the industrial revolution of production based on the innovative advancement of big data management and the cloud computing environment.
This special issue addresses the latest research advances into measurement for production engineering. This covers a wide area, including dimensional measurement, surface metrology, uncertainty, traceability, calibration, in-process and on-line metrology, machine tool metrology, optical metrology, micro and nano metrology, and applied sensor technology. We hope that learning more about these advances will enable the readers to share in the authors’ experiences and knowledge of technologies and development.
All papers were refereed through careful peer reviews. We would like to express our sincere appreciation to the authors for their submissions and to the reviewers for their invaluable efforts, ensuring the success of this special issue.
The optical frequency comb has become a standard for length and frequency measurements. Its pulsed laser can produce temporal coherence interference fringe patterns, and these fringes can be used as the length standard for practical measurement of absolute lengths. This research aims to develop a measuring system for coordinate measuring machine (CMM) verification, which can be used to measure the absolute length of a target in three dimensions. Thus, a spherical target has been considered. A ball lens with a refractive index of 2.0 has been selected as the target for the interferometer in this study. Using the ball lens target, the absolute length can be measured up to 10 m, covering the medium- to large-sized range of CMM applications. The experimental results demonstrate that the measurement uncertainty is smaller than that of the artifact test. In addition, the measurement time of the proposed method is 60% less than that of the artifact-test method.
One-dimensional grating is one of the most important standards that are used to calibrate magnification of critical-dimension scanning electron microscopes (CD-SEMs) in the semiconductor industry. Long-term stability of pitch calibration systems is required for the competence of testing and calibration laboratories determined in ISO/IEC 17025:2005. In this study, calibration and measurement capabilities of two types of pitch calibration systems owned by a calibration laboratory are re-evaluated through comparison to a reference value and its expanded uncertainty given by a metrological atomic force microscope (metrological AFM) at National Metrology Institute of Japan (NMIJ), AIST. The calibration laboratory’s pitch calibration systems are designed by using the diffraction method (optical and X-ray).
This paper presents a system for measuring a 3D microstructure using an optical-fiber probe. A stylus shaft was fabricated using an acid-etch technique.We investigated the process of fabricating a stylus tip using an adhesive method, an arc-discharge method, and a CO2-laser technique. The characteristics of the stylus shaft in the process of detecting the displacement were then described. Finally, in the case wherein the stylus tip was fabricated using an adhesive, the deformation of the stylus tip caused by the contraction of an ultraviolet curing resin, which was used to glue the stylus shaft to the stylus sphere, was analyzed using a finite-element method. Accordingly, a stylus shaft and tip with respective diameters of 0.4 μm or greater and 1 μm or greater were manufactured using the adhesive method. Moreover, the results helped confirm that stylus tips with diameters in the ranges of 20–196 and 1.2–300 μm were fabricated using the arc-discharge method and CO2-laser technique, respectively, with high yield. In addition, the results of the finite-element method revealed that the maximum elastic-deformation volume was approximately 0.8 nm and the effect of the contraction of the ultraviolet curing resin is minimal.
X-ray computed tomography systems (X-ray CT) designed for metrological use are frequently used in the manufacturing industry. This is because X-ray CT is able to measure not only outer geometry but also inner geometry nondestructively and relatively quickly. However, X-ray CT in the state of the art is not always able to demonstrate its measurement performance and traceability to SI. One of problems is that it is hard to evaluate error sources unique to X-ray CT, such as scattering and beam hardening, called as “material influence.” The hypothesis to the mechanism of Bi-directional length measurement error from the material influence is proposed. The hypothesis is that Bi-directional length measurement error is mainly caused by the form measurement error of a small feature on the gauge. The form measurement error of a small feature on the gauge is dominantly influenced by beam hardening. The hypothesis is validated through actual experiments and simulations. The results of the experiments and corresponding simulations lead us to the conclusion that the magnitude of the form measurement error of a small feature on a rotational asymmetric gauge is clearly correlated with a location of the small feature on the gauge.
Many error separation techniques to separate a surface profile from the parasitic motion of the instrument using multiple sensors and/or multiple scans have been proposed. In recent years, large-scale surface profile measurements have become required. When a measured surface profile is large, the number of sampling points becomes large. As the result, the influence of random error becomes large. Previously, a multi-step technique for the division of length was used to decide the short scale from the large scale. An important requirement of this multi-step technique for the division of length is to keep high accuracy at several key points. We applied this technique to the integration method for surface profile measurement and proposed a combination of the large-scale integration method and the short-scale integration method. The results of the theoretical analysis, simulation, and experiment show that this combination method decreases the influence of random error propagation for surface profile measurement.
Recently, the production of silicon wafers 450 mm in diameter has begun. However, a precise method for warp measurement of 450 mm wafers has not yet been established. Hence, the authors have developed a four-point-support inverting method to measure the warp shapes of large diameter wafers with high accuracy. The principle of this measurement method is equivalent to that for the three-point-support inverting method developed for warp measurement of 300 mm wafers. In the four-point-support inverting method, surface shape measurement can be performed with decreased deflection due to gravity using an additional central support. In this study, the principle of the proposed measurement method was verified experimentally. It was found that the four-point-support inverting method could measure the warp of a 300 mm wafer with high accuracy, equivalent to that of the three-point-support inverting method. However, in this experiment, a steel ball was used for additional support which caused concern regarding damage to the wafer surface at the point of contact with the support. Hence, a noncontact support method using an air bearing was proposed. It was found that the noncontact support method could measure the warp with accuracy equivalent to the contact support method described previously. Moreover, this study demonstrates the superiority of the four-point-support method to the three-point-support method regarding the repeatability of the warp measurement.
Interferometers are widely used to measure large aspheric surfaces because of their high accuracy and high efficiency. However, they cannot be used for aspheric surfaces with large curvature and asphericity. In this paper, we propose a method for measuring aspheric surfaces using scanning deflectometry with an autocollimator. A rotary stage is used to enlarge the measurement range of the autocollimator, so that aspheric surfaces with large slope changes can be measured. Three-dimensional error analysis is performed. We use an autocollimator with a measurement range of 21500 μrad (4500 arcsec) to measure a spherical surface with a curvature radius of 400 mm to perform the experiment. Experimental results showed that the average root-mean-square error was approximately 100 nm.
This study proposes a non-contact measurement method for evaluating a micro cutting tool diameter at a sub-micrometer precision in atmospheric environment. Practically, non-contact tool measurements are widely used in optical measurement methods. However, the generally used geometrical optical measurement methods do fundamentally not have sub-micrometer precision due to well-known light diffraction phenomenon, notably when measuring a micro tool. We have been proposing and developing a measurement method especially for the micro tool utilizing laser diffraction. In this study, we subtracted a transparent light component from a laser light distribution diffracted by the micro tool to be measured to enhance diffraction pattern characteristics. Consequently, micro rods having diameters of 15, 20, and 30 μm could be precisely measured. Furthermore, in order to verify the method validity, a two-helical-fluted micro tool (20 micrometer in diameter) was also measured while rotating (4 min-1) with less than 400 nm difference compared to images from a scanning electron microscopy (SEM) image. Finally, a trial to measure a micro drill diameter was also carried out during high-speed tool rotation (136,800 min-1) with our developed apparatus that is enough compact to be installed to machine tools, in order to perform the measurement in real rotation without stopping the tool rotation.
In planarization processes of sapphire, lapping process takes a long time because sapphire is a hard material. In contrast, superfinishing, which involves fixed abrasive machining, can substitute for lapping, and it would be possible to shorten the amount of processing time. In this work, vitrified-bonded diamond superabrasive stones with different grain diameters are developed. Then, multistage superfinishing is investigated by combining these stones. Results indicate that the multistage process is capable of producing a 2 nmRa surface, equivalent of a lapped surface in less than 10 min. To improve the process of multistage superfinishing, a removal amount estimation method is developed based on the real contact pressure calculation. The working area ratio of the stone was calculated by considering elastic deformation during superfinishing. The contact ratio of sapphire is calculated considering the roughness of the pre-finished surface and grain depth of cut. Accordingly, the real contact pressure is calculated to estimate the removal amount during superfinishing and finished surface roughness was expected.
In this study, a novel particle sizing method is proposed based on Brownian diffusion analysis for abrasive particles using fluorescent probing. A fluorescent probe is used to measure the average dynamic viscosity of the nanoparticle dispersion in a solvent. By measuring both the average dynamic viscosity and the size of the nanoscale abrasive particles simultaneously, the uncertainty of the particle sizing is considered to be improved based on the viscosity compensation for the Brownian diffusion of nanoparticles. In this research, the authors investigate the difference between the nanoviscosity and the shear viscosity of the solvent to verify the efficacy in using viscosity compensation for nanoparticle sizing.
To improve surface roughness, machining efficiency, and accuracy of a workpiece, measuring the roughness and contours of a cutting tool edge is crucial. However, it has not been easy for a contact stylus or non-contact methods to measure the roughness and contours of a sharp edge for two reasons: doing so damages the contact stylus and steep angles produce poor reflected rays for the non-contact method. A point autofocus probe (PAP) is widely used for the roughness and contour measurements of various precision machining surfaces. The authors have developed a new method of measuring a cutting tool edge, a method using PAP with three-axis liner stages and a rotary stage. In this study, a cutting tool edge for micro-fabrication was precisely measured, and the roughness relationships of the cutting tool edge and workpiece surface were quantitatively evaluated.
We proposed to utilize terahertz (THz) waves for the measurement of moisture content of pulp injection molding (PIM) pellets. We developed an automatic and non-destructive THz measurement system with a 0.1 THz source, pyroelectric detector, load cell, and step motor stage. As a first step, the correlation between THz transmittance and moisture content of the PIM product was studied. The results strongly suggest that the proposed method should be applicable to moisture content analysis of PIM products with better than 1% resolution and accuracy, which is much better than the previous studies with more expensive THz sources. Since the contents of pellets and products are the same, it is possible to estimate the moisture content in the pellets by designing similar apparatus. It should be noted that this method is applicable not only to PIM but also has many other applications.
Functional surfaces are in demand for recent value-added products. Stereolithography based on evanescent light has been proposed as a technique to fabricate surface nanostructures, but some fabrication error sources must be addressed. In-process measurement is an essential solution to improve the fabrication performance. For in-process measurement in stereolithography, the refractive index of resin is an inherent parameter for product and condition monitoring. This study proposes the in-process measurement of the refractive index of resin based on surface plasmon resonance (SPR). The optical phase response at SPR is highly sensitive to changes in the refractive index of resin but has a narrow sensing range. Therefore, we propose a substrate with a tunable sensing range using lanthanum-modified lead zirconate titanate (PLZT). The structural design was considered using numerical simulation. The SPR conditions were calculated with regard to thickness combinations of PLZT and metal (Ag) films. Depending on these combinations, a sensing range can be tuned on the order of 10-3 to 10-4 RIU with a sensitivity of 106 rad/RIU. However, to realize these performances, the manufacturing accuracy of Ag thin films must be better than 0.1 nm.
This paper presents an experimental study on a new concept of a surface defect detection method, in which surface defects will be detected by monitoring a change in heat flow between a micro thermal sensor and a smoothly-finished measuring surface such as magnetic disks, sapphire substrates and so on. In the proposed method, the micro thermal sensor is designed to detect surface defects without any contacts in between them. Since the change in heat flow across the gap is utilized, the method is expected to find out both the convex and concave defects. Searching for the possibility of the non-contact surface defect detection by the micro thermal sensor, in this paper, a simple heat transfer model is established to estimate the change in heat flow due to the change in gap between the measuring surface and the sensor surface. Some basic experiments are also carried out by using prototype micro thermal sensors, each of which is composed of a pair of electrodes and a thin metal film resistor, fabricated on both the silicon and glass substrates.
The objective of this research was to develop a three-dimensional (3D) reconstruction system based on a time-domain optical coherence tomography (OCT) microscope. One of the critical drawbacks of OCT microscopes is that their axial measurement ranges are typically limited by their depths of field (DOFs), which are determined by the numerical apertures of their objective lenses and the central wavelengths of their light sources. If a low-coherence interference fringe is far outside the DOF, the measurement accuracy inevitably decreases, regardless of how well-adjusted the reference mirror is. To address this issue and improve the axial measurement range of the OCT microscope in this study, an object-scanning measurement scheme involving a Linnik interferometer was developed. To calibrate the system in the proposed technique, image post-processing is performed for a well-conditioned state to ensure that a low-coherence interference fringe is generated within the DOF, enabling 3D objects with high-aspect-ratio structures to be scanned along the axial direction. During object-scanning, this state is always monitored and is corrected by adjusting the reference mirror. By using this method, the axial measurement range can be improved up to the working distance (WD) of the objective lens without compromising the measurement accuracy. The WD is typically longer than 10 mm, while the DOF of the microscope is around 0.01 mm in general, although it varies depending on the imaging system. In this report, the experimental setup of a 3D reconstruction system is presented, a series of experimental verifications is described, and the results are discussed. The axial measurement range was improved to at least 35 times that of a typical OCT microscope with identical imaging optics.
Optical energy propagates along metal surfaces as collective oscillations of free electrons when those surfaces are irradiated with optical waves in accordance with the resonant condition. The oscillations with electrical fields are called surface plasmon polaritons (SPPs) and are used in medium sensors. Here, using SPPs, the flow of a liquid–liquid two-phase fluid is visualized, and the flow-rate distribution is derived. A channel on a silver-film surface deposited on a glass slide is filled with an ethanol aqueous solution. SPPs are excited on the silver surface by a helium–neon laser. Then, water is injected into the channel in a laminar flow. As the water approaches the silver surface, the SPP excitation is disturbed. This disturbance is observed as decreasing reflectance, from which we can estimate the distance between the water layer and the silver surface. The method does not require any tracer particles or coloring even though the sample fluids are clear and colorless.
This paper presents a technique that employs a stroboscopic oblique-incidence interferometer to visualize the motion of a vibrating object with a rough surface. An oblique-incidence interferometer is well suited to the analysis of a rough surface and micro displacement because light-scattering is reduced when a surface is rough. However, when continuous light is used, the fringe pattern on the vibrating surface in the ultrasonic region can not be observed for the analysis of a micrometer resolution profile. To overcome this problem, pulsed light synchronized with a vibrating sample is employed as a light source using an acousto-optic modulator (AOM). The timing between the vibrating sample and the observation light is controlled using a common oscillator, so that the time-resolved behavior of the stator can be measured. We successfully detect the periodic movement of a fringe pattern for a vibrating ultrasonic motor using the interferometer.
We propose a dual-wavelength phase-shifting digital holography technique with four wavelength-multiplexed holograms based on phase-division multiplexing utilizing the 2π ambiguity and zeroth-order diffraction-image suppression. Zeroth-order wave suppression is implemented by introducing the averaging method. Its effectiveness is experimentally shown and numerically and quantitatively investigated. The numerical investigation demonstrates the tolerance of the proposed technique against incoherent light noise and changes in the reference wave intensity. The image quality in the proposed technique depends on the intensity ratio between the object and reference waves but does not degrade with constant changes in intensity. In contrast, a previously reported four-step dual-wavelength phase-shifting technique was affected by the factors described above.
Green Production has becoming increasingly important because of the growing need for sustainable development. Lean Production is one the most influential concepts in contemporary industrial management. The focus of Lean Production has been waste elimination and streamlining operations. Therefore, it is natural to seek alternatives for balancing or synergizing productivity gains with environmental friendliness by combining Green and Lean initiatives. However, Green and Lean practices may result in negative side effects. Such cases are mostly explained by dysfunctional assessments of effects. Sometimes, companies center on the positive effects, but hide or externalize negative trade-offs. Therefore, consistent assessment is critical to secure the achievement of Green and Lean objectives. An assessment has to consider all vital interdependencies between various effects. When enforced by law, it should respect all limitations and incentives set by regulators. To address these issues, an approach to integrated assessment of Green-Lean Production was conceptualized. Two fundamental strategic perspectives are considered for assessment: the product and operations views.
This study focuses on electrochemical machining as a method of processing sintered carbide at high speed. Previous studies have suggested the possibility of using electrochemical machining to achieve the high-speed machining of sintered carbide. However, there has been strong resistance from industry against bringing sintered carbide into contact with a conductive liquid. This is because the material quality of sintered carbide is degraded by the elution of Co when in contact with a conductive liquid. In previous reports, the authors have shown that it is possible to control the two modes of Co elution occurring during electrochemical machining: the elution from sintered carbide in contact with an electrolyte and the selective elution of Co arising from differences in the speeds of the dissolution of tungsten carbide and the elution of Co when sintered carbide is connected to an electrical source for processing. It is possible to control the elution of Co from sintered carbide in contact with an electrolyte by adding Co ions to the electrolyte, which increases the Co ion concentration. In addition, the excessive elution of Co can be prevented by using a bipolar electrical source for machining. Although we have shown that it is possible to carry out the electrochemical machining of sintered carbide without degrading its quality, the addition of large amounts of Co ions to the electrolyte is expensive. Therefore, we attempted to prevent the degradation in the quality of sintered carbide by adding iron ions instead of Co ions, and we confirmed that the addition of Fe ions has the desired effect. However, the Fe2+ ions in the solution are easily oxidized to Fe3+ ions with time, and the Fe3+ ions yield no protective effect for sintered carbide. In our previous report, we discussed a method to bring the electrolyte into contact with Fe to prevent the oxidation of Fe2+ ions to Fe3+ ions and proposed the use of an iron filter. In the present report, we verify the effect of the iron filter.
A prototype hybrid machine was manufactured by combining five-axis laminate-shaping and five-axis cutting, and a CAM was developed for additive manufacturing under simultaneous five-axis control. Using a CAD surface as a shape-model for the laminate-shaping, the reproducibility of a shape in laminate-shaping or cutting was successfully enhanced. Moreover, a combination process of laminate-shaping and cutting was successfully defined by decomposing a shape into multiple parts. The prototype machine and CAM developed were investigated in a case study, and their usability was confirmed.