Industrial production processes are becoming more difficult and complex because of the need to accept or react to global requirements for ecology, energy saving, downsizing, short lead times, information technology, etc. Metrology and inspection play very important roles in production processes because these must decide the final quality of manufactured industrial goods. Laser/optical metrology is widely used in industry to maintain meter definition traceability because it is, in principle, nondestructive. This makes laser metrology a candidate for use in final industrial inspection.
This special issue originated in Laser Metrology for Precision Measurement and Inspection in Industry 2014 (LMPMI2014), also the 11th IMEKO symposium. LMPMI2014 covers a very wide area, including precision engineering, dimensional measurement, shape measurement, micro/meso/nano metrology, interferometry, and standards and calibration technology. This IJAT special issue features papers selected from LMPMI2014. Advanced papers in this issue present the latest achievements in laser metrology ranging from basic research to actual industrial application. These papers should prove useful to readers seeking to share their industrial R&D knowledge and experience.
The important contributions of the authors and reviewers are most deeply appreciated and make this issue both fascinating and its ideas far-reaching.
Coordinate measurement machine (CMM) probing techniques can involve direct mechanical contact (e.g., tactile probing) or diverse non-contact principles (e.g., laser line scan probing). For some applications, contact methods are not capable of measuring fast enough to ensure 100% quality controlled parts. A laser line scanning probe uses a laser triangulation-based method to acquire 3D measurement points on a workpiece relative to a sensor. Mounting the sensor in a 3D coordinate frame, e.g., in a CMM provides enough information to fully examine the workpiece. These techniques are most commonly exploited in medical industry and industries involving plate materials. A high data density and measurement speed are significant advantages when measuring free-form surfaces by laser line scanning, making the process much more time-efficient. However, high-precision geometrical features (such as cylinders, spheres, etc.) must be measured for locating and aligning the free-form shapes. The accuracy of the equipment therefore has to be assessed. Probe Maximum Permissible Error (MPEP) values below 10 μm have been reported for cutting-edge laser line scanners. This paper compares the major influences on measurements on cylindrical features. First, the aspect-ratio limitations are considered by comparing two inherently different techniques. The stable inspection of reference features is important, while trying to maximize the spatial extent of the measured features. Second, the measurement method is analyzed in two ways: by using a limited sample of the features to increase stability and eliminate interference from neighboring features; by varying the number of scan tracks, which greatly affects the measurement time.
In this study, an improved MOEMS (micro-optical electronic mechanical system) accelerometer based on integrated grating with phase modulation is proposed. This device is composed of a laser diode, an optoelectronic processing circuit, a sensing chip (consisting of a piezoelectric translator), an integrated grating as a reflective mirror on a transparent substrate, and a mechanical part of a bulk silicon proof mass suspended by four cantilevers whose upper surface acted as another mirror. This device generates a series of interference fringes by two diffracted beams when illuminated with a coherent light source, whose intensities are modulated by the relative distance between the grating and the proof mass. The intensities of the interference fringes varied with alterations in the distance caused by external accelerations that are proportional to the acceleration. The magnitude of acceleration can be calculated by using a differential circuit detecting the distance. The modified structure introduced in this paper obtains high sensitivity and reduces cross-sensitivity between different sensitive axes. The experimental results before the simulation and theory analysis demonstrate that this modified MOEMS accelerometer has a good performance with higher static acceleration sensitivity of 3×103 V/g and very low crosstalk.
The optical frequency comb has a short pulse, broad spectra, many spectral lines, and high temporal coherency. In this paper, a new absolute length-measuring technique with a high resolution of 0.05 μm is developed by using the temporal-coherence interferometry of the optical comb. A new fiber Fabry-Perot etalon (etalon) of a free spectral range with a frequency of 15 GHz is developed to improve fine positioning in space, so a short translation stage of up to a 10 mm movement is realized for various ranges of length. Moreover, the interference fringe peak is automatically detected by developing a new analog electrical circuit. The ambiguity of the interference-fringe orders is determined by using the etalon at a frequency 14.9 GHz within a time of 1 second for various length ranges.
To realize an efficient high-mix low-volume production, improving the yield rate by reducing production flaws is an important technique. Manufacturing touch panel displays with large-scale wiring boards is a typical example of the high-mix low-volume production. The National Institute of Advanced Industrial Science and Technology (AIST) has proposed a laser assisted ink-jet printing (LIJ) technology, which can repair the flaws of circuits by a silver nanoparticle ink. To establish an in-process repairing system for a touch panel display, a first production flaw detecting system is necessary in combination with LIJ technology. Therefore, the aim of this study is to develop a new first production flaw detecting system, which detects flaws in a large-scale circuit quickly. In this report, we have covered the basic concept of the proposed system, and the details of some preliminary experiments conducted using the developed measurement system. The performance requirements for the first production flaw detecting system are discussed. The basic concept of the detecting system and optical set-up was finalized. A preliminary first production flaw detecting system with galvano-scanner and multi-photodiode array was developed to confirm its ability to detect flaws and pattern profile. Some basic experiments were conducted to check the performance of this system. A flaw was intentionally created by making a scratch on a circuit pattern; the experimental results showed that this flaw could be detected by the equipment. The height detection technique for this system and preliminary experiments conducted using the developed system are also covered in this report. By using the laser trigonometry method, the displacement of profile height was detected with sufficient accuracy.
This paper presents two up-to-date moiré techniques for deformation measurement based on the memory function of a laser scanning microscope (LSM). The two techniques are the LSM overlapping moiré method and the LSM secondary moiré method. The formation principles and the measurement principles of these two methods are presented and compared to those of the traditional scanning moiré method for the first time. The applicable conditions and characteristics of these three moiré techniques are analyzed. Some typical moiré fringes on a strain gauge, carbon fiber reinforced plastics, a polyimide film, and a silicon wafer are illustrated. Our proposed LSM overlapping moiré method and LSM secondary moiré method are able to expand the application range of the LSM in deformation measurement to the micron and the submicron scales.
At the National Institute of Metrology (NIM), China, the Small Angle Measuring System, which is based on the sine principle, was developed as the national primary standard for the plane angle in an angular measuring range of ±5°. The measurement uncertainty of this system is dominated by the accuracy of an invar angular interferometer optical system. To calibrate this angle interferometer system, a series of known reference standards were generated with a multi-step method using a double-deck rotary table. The measurement uncertainty of the calibration is estimated to be approximately 0.05” (k=2).
The peculiarities of 3D objects image formation with clear shadow projection based on the constructive theory of 3D objects formation under illumination by partially coherent and perfectly incoherent light are investigated. Threshold algorithms for determining the position of boundaries of geometric 3D objects are developed, algorithms taking into account object thickness, light source angular sizes, and projection system angular apertures. These algorithms are based on the application of a true (calculated) threshold or a standard one using the corrective component for thresholds. Cases of weak and strong 3D object volumetricity for partially coherent and incoherent illumination are studied. The analytical equations for these algorithms are given. It is shown that the use of algorithms can significantly improve the measurement accuracy of the extended objects.
Modern industry and science require novel 3D optical measuring systems and laser technologies with micrometer/nanometer resolutions. To solve actual problems, we have developed a family of these optical measuring systems and technologies. An optical system for the 3D inspection of ceramic parts is described. A new approach to the formation of 3D laser templates using diffractive optics is presented for large objects, such as ∼30 m antennas. The performance specifications of a 3D super resolution, optical low-coherent micro/nano profilometer are given. Using a perfectly smooth atomic mirror as a reference object, a breakthrough depth measurement with resolution of 20 picometers is achieved. The newest results in the field of laser technologies for the high-precision synthesis of microstructures by an updated laser circular image generator using the semiconductor laser is presented. The measuring systems and the laser image generator have been tested by customers and are used in different branches of industry and science.
Form and dimension measurements using X-ray computed tomography (X-ray CT) are useful in product development, reverse engineering, production control and quality certification. This is because X-ray CT systems can get three-dimensional 3D volumetric data on the full body of the target object all at once. The measurement space of 3D coordinate measuring systems (CMSs), which include X-ray CTs, are distorted by kinematic and other factors. This means that measurement space deformation should be compensated for precise dimensional measurement. The compensation function should also be occasionally checked. For the widely-used coordinate measuring machine (CMM), the mobile frame is stable over a long period, making it unnecessary to check whether the compensation function works well or not on the CMM. The mobile frame of the X-ray CT is less stable than that of a CMM, so the space deformation compensation function on X-ray CTs should be checked more often than that on CMMs to perform precise dimensional measurement using X-ray CTs. We propose a simple interim check method for an X-ray CT that is through repeated checking, assesses the long-term stability of the mobile frame of the X-ray CT.
Scanning probe CMMs have come to be considered the standard in coordinate metrology, not only because they provide high-quantity, high-speed data gathering but also because the scanning technology significantly decreases inspection time. Modern manufacturing, especially in today’s highly competitive economy, requires increasingly efficient measuring machines and processes because inspection machines have often become the bottlenecks in the entire manufacturing processes. More efficient coordinate metrology can mean faster measurement cycles with acceptable accuracies. However, increasing scanning speeds has also significantly increased errors. This article proposes a new method of investigating and identifying the principal components of CMM dynamic errors. The principle of the method is presented, and the validity of the method is experimentally confirmed on a bridge coordinate measuring machine.
Fluorescent polarization methods are used to detect complementary base pairing of DNA in biological fields. These methods work by measuring the rotational diffusion coefficient of Brownian motion of the fluorescent particles in solution. The rotational diffusion coefficient corresponds to the inverse third power of diameter according to the Debye-Stokes-Einstein equation for nanoparticles as hard spheres. We develop a novel method to measure the rotational diffusion coefficient using a fluorescent probe with a DNA spacer connected to a gold nanoparticle. We studied the physical characteristics of this probe to verify the feasibility of the proposed method. The rotational diffusion coefficients of gold nanoparticles with diameters ranging between 5–20 nm were measured using this developed system. In this manuscript we describe a novel fluorescent polarization method for nanoparticle sizing using a fluorescent DNA probe.
A calibrator for 2D grid plates have been developed. The calibrator was based on a commercial imaging coordinate measuring machine (imaging CMM). A laser interferometer for the calibration of the x-coordinate and two laser interferometers for the calibration of the y-coordinate were attached to the imaging CMM. By applying multistep measurement method for the calibration procedure, the geometrical error in the calibrator was reduced. The calibration of a precision 2D grid plate was demonstrated, and the expanded uncertainty was estimated to be 0.2 μm (k=2).
We propose a new calibration method for 3D laser measurement systems used for inspecting the insides of industrial parts such as vessels and pipes. We developed the proposed calibration system using a cylindrical artifact such that the calibration is simple and easy to perform. We simulated and analyzed the proposed cylindrical artifact calibration method and the results demonstrate its adequacy.
Displacement detection of a small sphere with high sensitivity is required for realizing the micro tactile probe used in micro-coordinate-measuring machines (CMMs). Therefore, the authors have proposed a new technique for detecting the three-dimensional displacement of a small sphere by a kind of astigmatic method, termed the “eccentric astigmatic method (EAM).” In the EAM, a spherical mirror as a spherical tactile probe is placed on the focus of an objective lens. At this position, three eccentric beams, focused by the objective lens, are incident on the mirror surface at right angles and the reflected rays return on the incident paths. In contrast, when the sphere moves from this position even by a small distance, the return path of each reflected ray changes drastically. This change can be detected by the EAM using a condenser lens and a photodetector. The changes in the spot radius caused by the EAM were calculated using a ray-tracing code. As a result, a change in the spot shape was found to occur only for displacement along one axis. Moreover, simulations based on wave optics were performed, whose results confirmed the feasibility of detection of the three-dimensional displacement of a sphere by the EAM.
The increasing quality expectations and the global competition push manufacturing industry to adopt strategies of lean manufacturing and precision engineering. In order to reach these aims it is necessary that the measuring process is integrated in the production chain to provide timely feedback for process control. Nowadays, however, forged products are typically measured after the cool-down process, which can take several hours. The advantages obtainable if forgings would be measured online are clear: deviations in the production process would be recognized earlier and the production process could be promptly adjusted. On-line measurement capabilities have the potential to reduce overall production costs and consequently are of interest to many forging industries, including those producing complex products such as turbine blades. Under these circumstances, the HOTGAUGE project was initiated: an international EUROSTARS project with the goal to develop a measuring system, capable of measuring freeform shaped parts at elevated temperature (approx. 800°C) directly after the forging step. The output of the measuring system is a 3D model of the hot part including temperature information. The 3D coordinate measuring system is composed by two main subsystems: a 2D laser-triangulation system capable to scan a complete section of the part, and a moving platform, which moves the part through the measuring plane. The architecture and the components of the measurement system as well as measurement results are presented in this paper.
Recently, a strong need has arisen for a dimensional X-ray computed tomography system that is capable of dimensional measurements. This is because the speedy realization of dimensional measurements for outward forms and inward forms on dense spatial points remarkably simplifies and accelerates production loop. However, although the image obtained via XCT describes the structure clearly and in great detail, dimensional metrology by means of XCT is not simple. The National Metrology Institute of Japan has been carrying out performance tests using gauges that include the gauges proposed in ISO10360. In this work, the magnification variation correction is carefully presented, and a maximum deviation of less than 5 μm is shown to be possible by means of the measurement of the forest phantom of 27 ruby spheres, the locations of which are calibrated by the coordinate measuring machine.
Chemical mechanical polishing (CMP) is one of the most important processes for fabricating highly planarized substrates such as sapphire for light emitting diodes (LEDs). However, sapphire is categorized as a hard-to-process material; therefore, a long processing time is required because of the low polishing efficiency (i.e., removal rate). This study investigates the CMP mechanism for hard-to-process materials using the following polishing evaluation parameters: (1) the velocity ratio, which is defined as the ratio of slurry flow velocity between the wafer and polishing pad during CMP to the pad tangential velocity, (2) the standard deviation of the velocity ratio distribution, and (3) the polisher vibration acceleration during CMP. Each parameter was measured at five rotational speeds and two polishing pressures for a total of ten conditions using a commercially available single-sided polisher. Moreover, the influence of each parameter on the removal rate was demonstrated via a multiple correlation analysis. As a result, we revealed that the velocity ratio and polisher vibration acceleration are strongly related with the removal rate.
Devices such as pyroelectric infrared sensors, ultrasonic sensors, cameras can be used to detect the presence of human-beings, but their systems have some problems related to low detection ability, low resolution, privacy, and high cost. We propose the use of thermopile infrared sensors without focus lenses and with high-gain amplifiers to detect the position and movement of human subjects. The system can detect even people that are not moving. This paper presents an approach that uses two thermopile sensors mounted on the ceiling to detect in 2D the position and orientation of human bodies. After each sensor takes measurements, we can build an approximate equation set that takes into account the output voltage, distance, and orientation of the human presence. The equation set can be solved, using the steepest descent method for the outputs of the two sensors, to obtain in real-time the position of a human-being in 2D. Body orientation can also be basically obtained by detecting slight changes in some positions while the human subject is moving. Tests are carried out to confirm that the proposed system works.
We propose a wide-range micro- and nano-positioning sensor based on an image sensor. The intensity distribution of a Moiré signal is measured on the image sensor and used for position sensing via Fast Fourier Transform (FFT) analysis. The FFT returns the frequency spectra and phase characteristics of the image. The frequencies caused by the beam divergence, the order of diffraction, and the Moiré signal can then be identified. The sensor can detect position with high accuracy using the phase shift of the Moiré signal. The results also demonstrate a measurement range of up to 6 mm and an estimated standard deviation of 3.3 nm under specified conditions. Moreover, the target position can be set arbitrarily by automatic PI control. This positioning sensor is characterized as using only one sensor to detect position with a high accuracy over a wide measurement range, making it easy to install in existing industrial machines and tools. Moreover, the accuracy and the measurement range are selectable by choosing the appropriate frequency component.