Dynamic frequency scanning interferometry measurement based on optical frequency synchronous motion measurement and error compensation

Frequency-scanning interferometry (FSI) utilizing external cavity diode lasers (ECDL) stands out as a potent technique for absolute distance measurement. Nevertheless, the inherent scanning nonlinearity of ECDL and phase noise pose a challenge, as it can compromise the accuracy of phase extraction from interference signals, thereby reducing the measurement accuracy of FSI. In this study, we propose a composite algorithm aimed at mitigating non-orthogonal errors by integrating the least-squares and Heydemann correction technique. Furthermore, we employ Kalman filtering for precise phase tracking. We introduce a parameter selection strategy based on the statistical distribution of instantaneous frequency to achieve the fusion estimation of phase observation values and theoretical models, which starts a new perspective for the application of multi-dimensional data fusion in FSI measurement. Through simulation and experimental validation, the efficacy of this approach is confirmed. The experimental results show promising outcomes: with an average phase error of 0.12%, a standard deviation of less than 1.7 µm in absolute distance measurement, and an average positioning accuracy error of 0.29 µm.

Absolute distance measurements could be achieved by the technique of frequency scanning interferometry (FSI), which could provide a micron-level accuracy over several tens of meters. However, as the scanning range and distance increasing, the measurement accuracy and resolution would be seriously influenced by the dispersion mismatch effect, which is mainly caused by the dispersion difference between optical fiber and air. A dispersion compensation method was proposed in this paper, and the mismatch effect would be suppressed effectively without complicated calculations for each single measurement. The chirp in resampling clock would be corrected with a pre-calibration procedure, and the compensation factor is demonstrated for different distances. A calibration method of dispersion compensation factor is also proposed, and the linear regression residual is employed as the criterion. Then, the compensation method is evaluated by experiments with different spatial distances and scanning ranges. Finally, a 60-m experiment is carried out for accuracy comparison, and the measurement accuracy is better than 15 µm by comparing with commercial interferometers.

Frequency-scanning nonlinearity fundamentally limits the ranging precision of frequency-scanning interferometry (FSI) systems based on external cavity diode lasers (ECDLs). To address this limitation, a frequency scanning nonlinearity suppression method based on a rate-dependent asymmetric Prandtl-Ishlinskii (RA-PI) model is proposed. By employing, for the first time, a phenomenological modeling approach, the rate-dependent and asymmetric nonlinear optical frequency response of the ECDL is accurately characterized. An inverse RA-PI model is derived and implemented as a feedforward compensator to linearize the frequency scanning. Experimental results show that the frequency-scanning linearity is improved by approximately one order of magnitude. Consequently, the maximum standard deviation of absolute distance measurements is reduced from 58.25 μm to 9.79 μm, and the maximum relative displacement deviation decreases from 42.97 μm to 11.56 μm. Furthermore, the velocity measurement precision for dynamic targets is improved by a factor of 2.61 to 5.75.

Frequency scanning interferometry (FSI) is a promising technique for absolute distance measurement and has been demonstrated in many industrial applications. However, in practice, the measurement precision is limited and sensitive to the variations of the measured distance while sweeping the optical frequency of the laser. The induced errors would be amplified by hundreds of times due to the magnification effect. In this paper, an incremental interferometer was established on the basic scheme of the FSI system for monitoring the variations of distance. The compensation could be achieved by multiplying the heterodyne signals from monitor and measurement interferometer without complex and time-costing data processing. The system performance has been verified by experiments for different kinds of vibrating targets. Finally, after compensation by suppression of the magnification effects, a measurement precision of 4.26 μm has been achieved in a range of 10 m.

The development and validation of a portable coordinate measurement solution for fiducialization of compact linear collider (CLIC) components is presented. This new solution addresses two limitations of high-accuracy state-of-the-art coordinate measuring machines, i.e. lack of portability and limited measurement volume. The solution is based on frequency scanning interferometry (FSI) distances and the multilateration coordinate measurement technique. The developments include a reference sphere for localizing the FSI optical fiber tip and a kinematic mount for repositioning the reference sphere with sub-micrometric repeatability. This design enables absolute distance measurements in different directions from the same point, which is essential for multilateration. A multilateration test bench built using these prototypes has been used to fiducialize a CLIC cavity beam position monitor and 420 mm-long main beam quadrupole magnet. The combined fiducialization uncertainty achieved is 3.5 μm (k = 1), which is better than the CLIC 5 μm (k = 1) uncertainty specification.

Norm and interpolation based absolute stress evaluation in steel members using the Lcr wave

Existing errors in the structure and kinematic parameters of multi-legged walking robots, the motion trajectory of robot will diverge from the ideal sports requirements in movement. Since the existing error compensation is usually used for control compensation of manipulator arm, the error compensation of multi-legged robots has seldom been explored. In order to reduce the kinematic error of robots, a motion error compensation method based on the feedforward for multi-legged mobile robots is proposed to improve motion precision of a mobile robot. The locus error of a robot body is measured, when robot moves along a given track. Error of driven joint variables is obtained by error calculation model in terms of the locus error of robot body. Error value is used to compensate driven joint variables and modify control model of robot, which can drive the robots following control model modified. The model of the relation between robot’s locus errors and kinematic variables errors is set up to achieve the kinematic error compensation. On the basis of the inverse kinematics of a multi-legged walking robot, the relation between error of the motion trajectory and driven joint variables of robots is discussed. Moreover, the equation set is obtained, which expresses relation among error of driven joint variables, structure parameters and error of robot’s locus. Take MiniQuad as an example, when the robot MiniQuad moves following beeline tread, motion error compensation is studied. The actual locus errors of the robot body are measured before and after compensation in the test. According to the test, variations of the actual coordinate value of the robot centroid in x-direction and z-direction are reduced more than one time. The kinematic errors of robot body are reduced effectively by the use of the motion error compensation method based on the feedforward.

Azorhizobium caulinodans is considered a highly promising microbe because of its ability to fix nitrogen in the free-living state as well as in symbiosis. Most of the estimates made for N2 -fixation by Azorhizobium—rice associations are based on acetylene-reduction assay, a method that has been questioned for accuracy in absolute measurements. The present work aimed at finding the effecitveness of this microorganism to increase N-content in four Pakistani cultivars of rice by comparing total nitrogen per plant.

Absolute distance measurement plays an important role in many areas, such as aerospace and scientific research. Traditional measurement methods generally cannot meet requirements for long-range and high-precision at the same time. In this paper, an absolute distance measurement method based on alternately oscillating optoelectronic oscillator is proposed. This method places the distance to be measured in the loop of optoelectronic oscillator and takes advantage of accumulative magnification effect to achieve high accuracy. The measurement and the reference optoelectronic oscillators are established and selected by an optical switch, and a microwave switch is used to choose the high-order or low-order oscillating frequency. The high-order frequency and low-order oscillating frequency of the measurement and reference optoelectronic oscillators are measured in turn by frequency counter to calculate the loop lengths of two optoelectronic oscillators. The low-order frequencies are used to measure the fundamental frequency roughly and the high-order frequencies are used to calculate loop length precisely. Although the mode hopping occurs in the measurement process, it does not affect the loop length calculation by substituting the corresponding oscillating mode number. Note that the loop length measurement moments of two optoelectronic oscillators are different due to the switching order of optical switch and microwave switch. In order to calculate the absolute distance, which is the length difference between two optoelectronic oscillators at the same moment, the measured loop lengths should be averaged.In this way, systematic error accumulation caused by slow drift of environment can be eliminated, and this method does not need to control the length of reference optoelectronic oscillator. Meanwhile, the measurement system is simple. In the experiment, 1 km, 5 km and 8 km fibers are placed in a common part of the measurement and reference optoelectronic oscillators to simulate different long-range distances in space. A high-resolution optical delay line is placed in the measurement optoelectronic oscillator to verify the performance of the measurement system. The experimental results show that the measurement error is 3.5 μm with a 3.5 μm maximum standard deviation of each measurement distance at an emulated round trip distance of 6 km. The relative measurement accuracy reaches 5.8 × 10<sup>－10</sup>. This method provides a feasible idea for solving the technical problems of long-range and high-precision absolute distance measurement.

This paper deals with video segmentation based on motion and spatial information. Classically, the nucleus of the motion term is the motion compensation error (MCE) between two consecutive frames. Defining a motion-based energy as the integral of a function of the MCE over the object domain implicitly results in making an assumption on the MCE distribution: Gaussian for the square function, Laplacian for the absolute value, or other parametric distributions for functions used in robust estimation. However, these assumptions are generally false. Instead, it is proposed to integrate a function of (an estimation of) the MCE distribution. The function is taken such that the integral is the Ahmad-Lin entropy of the MCE, the purpose being to be more robust to outliers. Since a motion-only approach can fail in homogeneous areas, the proposed energy is the joint entropy of the MCE and the object color. It is minimized using active contours.

With the rapid advancement in deep-space exploration, back-end systems such as Chirp Transform Spectrometers (CTS) must be equipped with larger bandwidths, higher frequency resolutions, and enhanced sensitivities. Phase errors in chirp signals distort pulse compression waveforms, significantly affecting CTS system performance. To correct the distorted pulses, we acquire a priori information about the pulse waveform by measuring the phase errors in the CTS system. This paper measures and analyzes phase errors in the expander and compressor signals of a 1GHz bandwidth CTS system. We discuss the impact of these phase errors on pulse waveforms, system frequency resolution, sensitivity, and other critical performance parameters. Additionally, we plot the in-band phase error curves for the system. By utilizing these phase error curves, we can determine the phase error for any input frequency, thereby providing valuable prior information for pulse compression waveform correction. This approach is crucial for guiding subsequent error optimization and compensation in the CTS system.

As mobiles become a ubiquitous, they are used more and more for operations that may involve sensitive data or huge amounts of money. The mobile is also increasingly being used as the tool of preference for browsing and using the Internet. Hence, new security measures must be developed to support increased functionality of these devices, to protect users in the case of any mishap. Authentication using keystroke dynamics for mobiles is an area that has received attention recently. In this paper, we have studied some authentication techniques used earlier including relative and absolute distance measures, mean and standard deviation based methods and feature fusion methods. We provide a method for authentication using fusion techniques for our own novel mean and standard deviation based approaches, which gives low error rates.

Absolute linear encoders have emerged as a core technical enabler in the fields of high-end manufacturing and precision displacement measurement, owing to their inherent advantages such as the elimination of the need for homing operations and the retention of position data even upon power failure. However, there remains a notable scarcity of comprehensive review materials that can provide systematic guidance for practitioners engaged in the field of absolute linear encoder measurement technology. The present study aims to address this gap by offering a practical reference to professionals in this domain. In this research, we first systematically delineate the three fundamental categories of measurement principles underlying absolute linear encoders. Subsequently, we analyze the evolutionary trajectory of coding technologies, encompassing the design logics and application characteristics of quasi-absolute coding (including non-embedded and embedded variants) as well as absolute coding (covering multi-track and single-track configurations). Furthermore, we summarize the primary error sources that influence measurement accuracy and explore the operational mechanisms of various types of errors. This study clarifies the key technical pathways and existing challenges associated with absolute linear encoders, thereby providing practitioners in relevant fields with a decision-making guide for technology selection and insights into future development directions. Moving forward, efforts should focus on achieving breakthroughs in critical technologies such as high fault-tolerant coding design, integrated manufacturing, and error compensation, so as to advance the development of absolute linear encoders toward higher precision, miniaturization, cost reduction, and enhanced reliability.

We are evaluating the usefulness of stereomammography in improving breast cancer diagnosis. One area that we are investigating is whether the improved depth perception associated with stereomammography might be significantly enhanced with the use of a virtual 3D cursor. A study was performed to evaluate the accuracy of absolute depth measurements made in stereomammograms with such a cursor. A biopsy unit was used to produce digital stereo images of a phantom containing 50 low contrast fibrils (0.5 mm diam monofilaments) at depths ranging from 1 to 11 mm, with a minimum spacing of 2 mm. Half of the fibrils were oriented perpendicular (vertical) and half parallel (horizontal) to the stereo shift direction. The depth and orientation of each fibril were randomized, and the horizontal and vertical fibrils crossed, simulating overlapping structures in a breast image. Left and right eye images were generated by shifting the x-ray tube from +2.5 degrees to -2.5 degrees relative to the image receptor. Three observers viewed these images on a computer display with stereo glasses and adjusted the position of a cross-shaped virtual cursor to best match the perceived location of each fibril. The x, y, and z positions of the cursor were indicated on the display. The z (depth) coordinate was separately calibrated using known positions of fibrils in the phantom. The observers analyzed images of two configurations of the phantom. Thus, each observer made 50 vertical filament depth measurements and 50 horizontal filament depth measurements. These measurements were compared with the true depths. The correlation coefficients between the measured and true depths of the vertically oriented fibrils for the three observers were 0.99, 0.97, and 0.89 with standard errors of the estimates of 0.39 mm, 0.83 mm, and 1.33 mm, respectively. Corresponding values for the horizontally oriented fibrils were 0.91, 0.28, and 0.08, and 1.87 mm, 4.19 mm, and 3.13 mm. All observers could estimate the absolute depths of vertically oriented objects fairly accurately in digital stereomammograms; however, only one observer was able to accurately estimate the depths of horizontally oriented objects. This may relate to different aptitudes for stereoscopic visualization. The orientations of most objects in actual mammograms are combinations of horizontal and vertical. Further studies are planned to evaluate absolute depth measurements of fibrils oriented at various intermediate angles and of objects of different shapes. The effects of the shape and contrast of the virtual cursor and the stereo shift angle on the accuracy of the depth measurements will also be investigated.

Dynamic absolute distance measurement by frequency sweeping interferometry based Doppler beat frequency tracking model