Holographic interferometric vibration measurement based on photorefractive crystal in diffusion mode.

A dynamic holographic vibration measurement system based on a photorefractive crystal of BSO in diffuse mode without the need for an external electric field, which allows for simultaneous measurement of in-plane and out-of-plane high-frequency vibrations, is studied theoretically and experimentally in this work. By adjusting the polarization state of the reference beam, the system introduces a necessary additional phase shift of π/2 to achieve highly sensitive and linear demodulation of small phase-to-intensity vibration signals. Both theoretical analysis and experimental results confirm the system's practicality and safety, demonstrating its ability to accurately detect vibrations without the risks associated with high-voltage drift mode operation.

Analysis and experimental verification of the polarization characteristics of cube-corner reflectors.

The polarization effect of cube-corner reflectors (CCRs), which influences the performance of optical systems, requires comprehensive analysis. This study developed a model for the polarization state of uncoated solid and hollow CCRs using the Jones matrix derivation and Zemax software simulations. The accuracies of theoretical analyses and simulations were verified using an experimental setup.

A comprehensive laser image dataset for real-time measurement of wheelset geometric parameters.

Railway transportation has experienced significant growth worldwide, offering numerous benefits to society. Most railway accidents are caused by wheelset faults so it's significant to monitor wheelset conditions. Therefore, we need to collect wheelset images, repaint them, extract laser stripe centerlines, construct 3D contour, and measure their geometric parameters to judge the wheelset's conditions.

Interferometric polarization compensation based on one single polarization-maintaining fiber.

In an interferometry system based on one single polarization-maintaining fiber (PMF), defects like the laser's ellipticity, the alignment error between the PMF and the laser source, and the PMF's internal stress will cause the emitted light from the PMF to be incompletely linearly polarized, resulting in nonlinear errors that cannot be ignored. This paper proposes a novel method that can realize polarization compensation for heterodyne interferometry, reduce the ellipticity of the emitted light, and thereby reduce the nonlinear error of the system. When using a PMF with an Extinction Ratio (ER) of 22 dB, the experimental results show that this method can reduce the polarization and increase the ER to 33.

Photoelectric Measurement and Sensing: New Technology and Applications.

Laser-based measurement and sensing technology has been paid more and more attention by academia and industry because of its incomparable advantages, such as high sensitivity, fast response, and no contact [...

Method and system for simultaneously measuring six degrees of freedom motion errors of a rotary axis based on a semiconductor laser.

The rotary axis is the basis of rotational motion. The motion errors of a rotary axis have an extremely important impact on the accuracy of precision machining measuring equipment such as CNC machines, robot manipulators, and laser trackers. It is a difficult problem to realise the fast and precision simultaneous measurement of multi-degree-of-freedom motion errors of a rotary axis.

High-precision method for simultaneously measuring the six-degree-of-freedom relative position and pose deformation of satellites.

The high-precision measurement of the six degrees-of-freedom (6DoF) relative position and pose deformation of satellites on the ground in vacuum and high-/low-temperature environments plays a critical role in ensuring the on-orbit mapping accuracy of satellites. To meet the strict measurement requirements for a satellite of a high accuracy, high stability, and a miniaturized measurement system, this paper proposes a laser measurement method for simultaneously measuring 6DoF relative position and attitude. In particular, a miniaturized measurement system was developed and a measurement model was established.

Error Analysis of Heterodyne Interferometry Based on One Single-Mode Polarization-Maintaining Fiber.

Using polarization-maintaining fiber (PMF) in dual-frequency heterodyne interferometry has the advantages of reducing the laser's own drift, obtaining high-quality light spots, and improving thermal stability. Using only one single-mode PMF to achieve the transmission of dual-frequency orthogonal, linearly polarized beam requires angular alignment only once to realize the transmission of dual-frequency orthogonal, linearly polarized light, avoiding coupling inconsistency errors, so that it has the advantages of high efficiency and low cost. However, there are still many nonlinear influencing factors in this method, such as the ellipticity and non-orthogonality of the dual-frequency laser, the angular misalignment error of the PMF, and the influence of temperature on the output beam of the PMF.

Recent Advances in Wayside Railway Wheel Flat Detection Techniques: A Review.

Wheel flats are amongst the most common local surface defect in railway wheels, which can result in repetitive high wheel-rail contact forces and thus lead to rapid deterioration and possible failure of wheels and rails if not detected at an early stage. The timely and accurate detection of wheel flats is of great significance to ensure the safety of train operation and reduce maintenance costs. In recent years, with the increase of train speed and load capacity, wheel flat detection is facing greater challenges.

Speckle Measurement for Small In-Plane Vibration Using GaAs.

In this study, the measurement characteristics of speckles based on the photoinduced electromotive force (photo-emf) effect for high-frequency, small-amplitude, and in-plane vibration were theoretically and experimentally studied. The relevant theoretical models were utilized. A GaAs crystal was used as the photo-emf detector for experimental research, as well as to study the influence of the amplitude and frequency of the vibration, the imaging magnification of the measuring system, and the average speckle size of the measuring light on the first harmonic of the induced photocurrent in the experiments.

Simultaneous measurement of 5DOF spindle error motions in CNC machine tools.

We present a method for the simultaneous measurement of 5 degree-of-freedom (DOF) spindle error motions in computer numerical control (CNC) machine tools and develop a measurement system. The measurement system uses polarization-maintaining fiber coupled with a dual-frequency laser as the light source. The axial error motion of the spindle is measured by heterodyne interferometry, and other 4DOF error motions are obtained by collimation measurement.

On-Site Calibration Method for Line-Structured Light Sensor-Based Railway Wheel Size Measurement System.

Line-structured light has been widely used in the field of railway measurement, owing to its high capability of anti-interference, fast scanning speed and high accuracy. Traditional calibration methods of line-structured light sensors have the disadvantages of long calibration time and complicated calibration process, which is not suitable for railway field application. In this paper, a fast calibration method based on a self-developed calibration device was proposed.

In-Service Detection and Quantification of Railway Wheel Flat by the Reflective Optical Position Sensor.

Railway wheel tread flat is one of the main faults of railway wheels, which brings great harm to the safety of vehicle operation. In order to detect wheel flats dynamically and quantitatively when trains are running at high speed, a new wheel flat detection system based on the self-developed reflective optical position sensor is demonstrated in this paper. In this system, two sensors were mounted along each rail to measure the wheel-rail impact force of the entire circumference by detecting the displacement of the collimated laser spot.

Simultaneous Measurement of 6DOF Motion Errors of Linear Guides of CNC Machine Tools Using Different Modes.

Based on the prior work on the six degrees of freedom (6DOF) motion errors measurement system for linear axes, and for the different types of machine tools and different installation methods, this study used a ray tracing idea to establish the measurement models for two different measurement modes: (1) the measurement head is fixed and the target mirror moves and (2) the target mirror is fixed and the measurement head moves. Several experiments were performed on the same linear guide using two different measurement modes. The comparative experiments show that the two measurement modes and their corresponding measurement models are correct and effective.

A Rail Fastener Tightness Detection Approach Using Multi-source Visual Sensor.

At present, the method of two-dimensional image recognition is mainly used to detect the abnormal fastener in the rail-track inspection system. However, the too-tight-or-too-loose fastener condition may cause the clip of the fastener to break or loose due to the high frequency vibration shock, which is difficult to detect from the two-dimensional image. In this practical application background, 3D visual detection technology provides a feasible solution.

A High-Precision Method for Dynamically Measuring Train Wheel Diameter Using Three Laser Displacement Transducers.

Wheel diameter is a significant geometric parameter related to the safe operation of trains, and needs to be measured dynamically. To the best of the authors' knowledge, most existing dynamic measurement methods and systems do not meet the requirement that the wheel diameter measurement error for the high-speed vehicle is less than 0.3 mm.

Railway Wheel Flat Detection System Based on a Parallelogram Mechanism.

Wheel flats are a key fault in railway systems, which can bring great harm to vehicle operation safety. At present, most wheel flat detection methods use qualitative detection and do not meet practical demands. In this paper, we used a railway wheel flat measurement method based on a parallelogram mechanism to detect wheel flats dynamically and quantitatively.

A Method for Simultaneously Measuring 6DOF Geometric Motion Errors of Linear and Rotary Axes Using Lasers.

A novel method for simultaneously directly measuring six-degrees-of-freedom (6DOF) geometric motion errors of CNC machine tools was proposed, and a corresponding measurement system was developed. This method can not only be applied for measuring a linear axis, but also for a rotary axis. A single-mode fiber was used to separate the measuring unit from the laser source in order to ensure system thermal stability and measurement accuracy.

Long-Term Stable Online Acetylene Detection by a CEAS System with Suppression of Cavity Length Drift.

A trace acetylene (C₂H₂) detection system was demonstrated using the cavity-enhanced absorption spectroscopy (CEAS) technique and a near-infrared distributed feedback (NIR-DFB) laser. A Fabry⁻Perot (F⁻P) cavity with an effective optical path length of 49.7 m was sealed and employed as a gas absorption cell.

Method for simultaneous measurement of five DOF motion errors of a rotary axis using a single-mode fiber-coupled laser.

The rotary axis is the basis for rotational motion. Its motion errors have critical effects on the accuracy of the related equipment, such as a five-axis computer numerical control machine tool. There are several difficult problems in the implementation of high-precision and fast measurement of the multi-degree-of-freedom motion errors of a rotary axis.

Measurement system and model for simultaneously measuring 6DOF geometric errors.

A measurement system to simultaneously measure six degree-of-freedom (6DOF) geometric errors is proposed. The measurement method is based on a combination of mono-frequency laser interferometry and laser fiber collimation. A simpler and more integrated optical configuration is designed.

System for simultaneously measuring 6DOF geometric motion errors using a polarization maintaining fiber-coupled dual-frequency laser.

A novel method for simultaneously measuring six degree-of-freedom (6DOF) geometric motion errors is proposed in this paper, and the corresponding measurement instrument is developed. Simultaneous measurement of 6DOF geometric motion errors using a polarization maintaining fiber-coupled dual-frequency laser is accomplished for the first time to the best of the authors' knowledge. Dual-frequency laser beams that are orthogonally linear polarized were adopted as the measuring datum.

Compensation for straightness measurement systematic errors in six degree-of-freedom motion error simultaneous measurement system.

The straightness measurement systematic errors induced by error crosstalk, fabrication and installation deviation of optical element, measurement sensitivity variation, and the Abbe error in six degree-of-freedom simultaneous measurement system are analyzed in detail in this paper. Models for compensating these systematic errors were established and verified through a series of comparison experiments with the Automated Precision Inc. (API) 5D measurement system, and the experimental results showed that the maximum deviation in straightness error measurement could be reduced from 6.

Rice (Oryza sativa L) plantation affects the stability of biochar in paddy soil.

Conversion of rice straw into biochar for soil amendment appears to be a promising method to increase long-term carbon sequestration and reduce greenhouse gas (GHG) emissions. The stability of biochar in paddy soil, which is the major determining factor of carbon sequestration effect, depends mainly on soil properties and plant functions. However, the influence of plants on biochar stability in paddy soil remains unclear.

Continual mechanical vibration trajectory tracking based on electro-optical heterodyne interferometry.

Vibration is one of the confused problems in many fields. To give a comprehensive analysis of vibration, an electro-optical heterodyne interferometry with temporal intensity analysis method that can track the trajectory of the vibration dynamically has been built in this paper. The carrier frequency is introduced by the electrically controlled electro-optical frequency shifter.