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In this paper, a novel, compact, and high-precision axial error measurement using a frequency-modulated interferometer is developed. Normally, heterodyne interferometers are a powerful system for small displacement measurements due to their property of being less sensitive to temperature and pressure variations. However, the maximum measurement speed of the heterodyne interferometer is around 5 m/s because it is usually limited by the difference in frequency between the two components of the laser beam, which is no larger than 3 MHz or 20 MHz corresponding laser source based on the Zeeman effect and acousto-optic modulator, respectively. The proposed measuring system is realized by modulating the frequency of the laser diode source at a high modulation frequency and using lock-in amplifiers to extract the harmonics of the interference signal. The measurement speed is proportional to the modulation frequency. Thus, the higher the modulation frequency, the higher the measuring speed attains. The frequency-modulated interferometer is then applied to measure the axial error of an ultra-precision spindle. The proposed system can be a capable solution for noncontact and high-precision spindle error measurements in the machining process.

The measurement speed and measurement accuracy of a displacement measuring interferometer are key parameters. To verify these parameters, a fast and high-accuracy motion is required. However, the displacement induced by a mechanical actuator generates disadvantageous features, such as slow motion, hysteresis, distortion, and vibration. This paper proposes a new method for a nonmechanical high-speed motion using an electro-optic modulator (EOM). The method is based on the principle that all displacement measuring interferometers measure the phase change to calculate the displacement. This means that the EOM can be used to accurately generate phase change rather than a mechanical actuator. The proposed method is then validated by placing the EOM into an arm of a frequency modulation interferometer. By using two lock-in amplifiers, the phase change in an EOM and, hence, the corresponding virtual displacement could be measured by the interferometer. The measurement showed that the system could achieve a displacement at 20 kHz, a speed of 6.08 mm/s, and a displacement noise level &lt, 100 pm//√Hz above 2 kHz. The proposed virtual displacement can be applied to determine both the measurement speed and accuracy of displacement measuring interferometers, such as homodyne interferometers, heterodyne interferometers, and frequency modulated interferometers.

In this manuscript, an automatic system for the real-time detection of focal position on a specimen during laser micromachining is presented. The system allows for accurately and rapidly positioning the laser focus on the target surface, wherever it is located along the optical axis. This approach is based on a feedback system that uses a laser source, actuator, focusing lens, specimen and camera to monitor the size of the beam spot. We propose a system to automatically find the focal point of laser by directly observing the shape, size and position of the beam spot on the surface through image processing. Compared with conventional methods, this approach is advantageous because the implementation is simple, easy and inexpensive. The results indicate dramatically high precision. The focal spot analytically maintains its size with a size deviation \(\pm 10{ \upmu {\rm m}}\).

Non-contact 3D shape measurement has been widely studied and applied to many fields of science and engineering owing to high speed, high accuracy, and simple implementation. However, the measurement system still poses improper acquisition of optical signal when surfaces with high reflectivity are scanned. This paper proposes a new and effective approach to solve the problem of shiny mechanical surface measurement. The appropriate exposure time for the surface measurement is indicated through image intensity histogram analysis. The appropriate exposure times in each region of the histogram are determined. Then, point clouds are merged at appropriate exposure times to obtain a good quality point cloud, avoiding the saturation region on the CCD. Profile parts of two different aluminum surfaces are measured fast and accurately using single exposure time and proposed solution. Experimental results prove that the proposed technique can inspect the 3D surface of the mechanical parts with high surface reflectivity.

This work presents the numerical analysis and validation of a fixed bed reactor model for 2,3-butanediol (2,3-BDO) dehydration. The 1D heterogeneous reactor model considering interfacial and intra-particle gradients, was simulated and numerical analysis of the model was conducted to understand the characteristics of the reactions in a catalyst along the reactor length. The model was also validated by comparing predicted performance data with pilot-scale plant data operated at 0.2 bar, 299–343 °C and 0.48–2.02 h−1 of weight hourly space velocity (WHSV). The model showed good agreement with the temperature profile, 2,3-BDO conversion and selectivity of target products. In addition, sensitivity analyses of the model were investigated by changing feed flow rate, feed composition, and inlet temperature. It was found that stable and efficient operation conditions are lower than 0.65 h−1 of WHSV and 330–340 °C of inlet temperature. Additionally, the reactor performance was not affected by 2,3-BDO feed concentration above 70%.

The interaction between a metal surface and multiple pulses was investigated to achieve optimal focusing conditions during ultrashort laser ablation. We report a simple theoretical expression of morphological changes in the ablated channel and demonstrate its advantage in positioning the interactive surface at the focus in real time during multiple-pulse laser ablation of a metallic material. Experimental results on the ablation depth for zinc, nickel, and copper show that the combination of a dynamic focusing system and a theoretical formula of ablation-cycle-dependent ablation depth enables one to control the shape of ablated channels. This model can be applied to a variety of high-efficiency ablation systems and may play an essential role in the development of a high-precision ablation system for the curved surfaces in highly scaled metal gravures used in printed electronics, which currently present challenges for engineers and technicians.

This paper presents a method for estimating vehicle speed using two roadside passive infrared (PIR) sensors whose optical axes are parallel to each other and perpendicular to the moving direction of vehicles. The vehicle speed was calculated based on the time lag between the two signals received by the PIR sensors, which was evaluated by using cross-correlation analysis. The experiments show that the method has an error of less than 5 km/h over a speed range of 20–60 km/h.

This paper proposes a method for high-precision radius measurements. The proposed system uses a frequency-modulation technique to improve the accuracy of detecting cat’s eye and the confocal position of a lens. The distance between two points defined as the radius of a lens was measured by using a frequency-modulated Michelson interferometer. In the confocal part, when the tested lens was moved along the optical axis, the intensity at the detector reaches a maximum at the confocal and cat’s eye positions of the sphere. Synchronous detection technique is used to turn the intensity signal from the detector into an odd-symmetry signal through a zero point. These symmetry points coincide with cat’s eye and confocal positions and thus enhance the accuracy with which these two points are detected. A frequency-modulated Michelson interferometer is used to accurately measure the displacement when moving the test sphere between the confocal and cat’s eye points.

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I2 hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I2 hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I2 absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I2 hyperfine transition at a high modulation frequency.