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The photoelectric sensing unit in a large-space measurement system primarily determines the measurement accuracy of the system. Aiming to resolve the problem whereby existing sensing units have difficulty accurately measuring the hidden points and free-form surfaces in large components, in this study, we designed a multi-node fusion of a combined sensor. Firstly, a multi-node fusion hidden-point measurement model and a solution model are established, and the measurement results converge after the number of nodes is simulated to be nine. Secondly, an adaptive front-end photoelectric conditioning circuit, including signal amplification, filtering, and adjustable level is designed, and the accuracy of the circuit function is verified. Then, a nonlinear least-squares calibration method is proposed by combining the constraints of the multi-position vector cones, and the internal parameters of the probe, in relation to the various detection nodes, are calibrated. Finally, a distributed system and laser tracking system are introduced to establish a fusion experimental validation platform, and the results show that the standard deviation and accuracy of the three-axis measurement of the test point of the combined sensor in the measurement area of 7000 mm × 7000 mm × 3000 mm are better than 0.026 mm and 0.24 mm, respectively, and the accuracy of the length measurement is within 0.28 mm. Further, the measurement accuracy of the hidden point of the aircraft hood and the free-form surface is better than 0.26 mm, which can meet most of the industrial measurement needs and expand the application field of large-space measurement systems. [ABSTRACT FROM AUTHOR]

Mode matching has proven effective in suppressing the mode hopping in external cavity diode lasers (ECDLs) without antireflection coating. However, prolonged operation of ECDLs is susceptible to mode hopping induced by fluctuations in the equivalent internal cavity length. In this study, we introduce a rapid mode hopping identification method by monitoring the first derivative of the frequency scanning interference signal. Subsequently, an adaptive mode hopping suppression method, based on the acquisition of a priori knowledge for the initial current traversal optimization range, is applied to ECDLs. The experimental results demonstrate a significant extension in the stable operation time of the ECDL by a factor of 17, surpassing 7 h using the proposed rapid adaptive mode hopping suppression method. [ABSTRACT FROM AUTHOR]

The measurement of distance plays an integral part in many aspects of modern societies. In this paper an integrated mode-locked laser on a chip is used for distance measurement based on mode-resolved interferometry. The emission from the on-chip source with a repetition rate of 2.5 GHz and a spectral bandwidth of 3 nm is coupled into a Michelson interferometer. The interferometer output is recorded as a spectral interferogram, which is captured in a single camera image. The images are analyzed using Hilbert transform to extract the distance. The distance derived shows a deviation of 6 $\mu$ m from the reference, for a distance up to 25 mm. We also demonstrate interferometry with repetition frequency sweep which can also be used with the source. Performance is expected to be better in the near future with the rapid developments in the field of on-chip laser sources which are demonstrating larger spectral widths and coherence lengths. [ABSTRACT FROM AUTHOR]

Frequency-scanning interferometry (FSI) using an external cavity diode laser (ECDL) is essential for many applications of the absolute distance measurement. However, owing to the hysteresis and creep of the piezoelectric actuator inherent in the ECDL, the optical frequency scanning exhibits a nonlinearity that seriously affects the phase extraction accuracy of the interference signal and results in the reduction of the measurement accuracy. To suppress the optical frequency nonlinearity, a harmonic frequency synthesis method for shaping the desired input signal instead of the original triangular wave is presented. The effectiveness of the presented shaping method is demonstrated through the comparison of the experimental results. Compared with an incremental Renishaw interferometer, the standard deviation of the displacement measurement of the FSI system is less than 2.4 μm when driven by the shaped signal. [ABSTRACT FROM AUTHOR]

Graphene(RGO)//[N-butyl-3,6-carbazolevinylene-alt-(2,5-dioctyloxy)-p-phenylenevinylene] (PPH-CAR) ternary nanocomposite is fabricated by a simple two-step method, which includes electrochemical reduction of graphene oxide (GO) and oxidation of simultaneously and an ultrathin PPH-CAR layer coated on the RGO/ surface. The structure of the composite is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM). The results suggest that the composite is correctly synthesized and each component has good dispersion. Cycle voltammetry (CV), charge and discharge measurements and cycle stability test are used to evaluate its electrochemical performance. Because of the synergistic effect of each component, the composite exhibits excellent electrochemical properties with specific capacitance of 175 F/g, which is a 46% increase compared with RGO/. Moreover, it reveals outstanding cycling performance with more than 90% capacitance retention over 1000 cycles. Such ternary composite is a candidate for high performance supercapacitors with great promise. RGO/MnO2/PPH-CAR ternary nanocomposite was successfully fabricated via a simple two-step method. The electrochemical performance of the composite was measured and the results show great improvement in conductivity, specific capacitance and Nyquist impedance. It is indicating that the conducting polymer offers interparticle connectivity and facilitates electron transport among each component. The improved electrochemical properties of the composite are attributed to the synergistic effect of each component and this kind of ternary composite is a promising candidate for high performance of electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

A ternary nanostructure, composed of graphite oxide (GO), MnO2 and poly[(2,5-di-phenyl-1,3,4-oxadiazole)-4-diylvinylene-alt-3,6-(N-butyl-carbazolenevinylene)] (POXA-CAR), is fabricated via a simple two-step method. The as-prepared composite is characterised by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and cyclic voltammetry. The specific capacitance of the composite electrode reached 310 F/g at a charging current of 2.5 mA, which is attributed to the synergistic effects from each component. GO has a large surface area and great mechanical properties. The conducting polymer provides electron transport path and partakes of the charge storage process. This Letter suggests that the ternary composite is a promising candidate for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract We propose a frequency-sweeping interferometry (FSI) with single external cavity diode laser that can be used to measure the absolute distances of a dynamic target. Generally, the FSI-Doppler effect induced by target drift restricts the measurement accuracy severely, but the Doppler effect can also be used to measure the actual movement during optical frequency sweeps. Thus, a mathematical model of the Doppler effect in FSI is presented and a novel FSI method based on Doppler beat frequency tracking model is proposed to realize the absolute distance measurement of a dynamic target. The method was verified successfully by measuring vibrating targets of 50 ∼ 5000 Hz at 38 mm in the laboratory. [ABSTRACT FROM AUTHOR]

Stereo vision measurement system is widely used in aerospace manufacturing, intelligent robot and other fields because of its unique advantages. However, when using the stereo vision measurement system for measurement, there is no guidance for the parameter configuration of the measurement system for the scene and task constraints, resulting in the stereo vision measurement system cannot play the maximum performance. In this paper, from two aspects of local measurement of camera parameters and global measurement of system parameters, the relevant model is established to analyze the measurement performance of a single independent camera and the performance of the whole stereo vision measurement system. Firstly, the relationship between single camera calibration parameters and measurement accuracy is analyzed; secondly, the relationship between stereo measurement system parameters and measurement accuracy is analyzed; finally, the stereo vision measurement error function is established to guide the design of measurement system parameters. According to the actual measurement experiment, the correctness of the analysis and the accuracy of the established function are verified, it is efficiently used for guiding the parameter design and camera selection of the measurement system in different measurement scene and task. [ABSTRACT FROM AUTHOR]

A particle-filter-based data processing for a frequency-scanning interferometry system for dynamic long absolute ranging is presented in this paper. Because the particle filter is not restricted by linearity or noise Gaussianity requirements, the proposed system achieves high robustness and accuracy levels when tracking dynamic objects at long standoff distances. We experimentally demonstrate that the proposed system exhibits a standard deviation below 6 μm for a quasi-static target, and superior tracking performance for a vibrating target with vibration amplitude exceeding 10 μm and frequencies of 1-5 Hz at a 15 m standoff distance.

A new frequency-scanning interferometry (FSI) scheme using in-phase and quadrature (IQ) detection for real-time and rapid absolute optical ranging is presented. Dynamic measurement with FSI modulates interference signal frequency by both target movement and time-varying optical-frequency scanning rate; hence, a dynamic model is proposed to decouple dynamic absolute distance from the instantaneous frequency of interference signals. The unscented Kalman filter and particle filter algorithms are implemented for the nonlinear first-layer and non-Gaussian second-layer models, respectively. The proposed FSI scheme eliminates nonlinear optical-frequency scanning effects in dynamic measurements and realizes real-time measurement only current observed data are used. Experimental results verify high tracking performance for a vibrating target with approximately 10 μm amplitude and 50-500 Hz frequency.

Nonlinear optical frequency scanning is inevitable in frequency scanning interferometry with tunable lasers and seriously reduces the accuracy of interference signal phase extraction. To address this, we propose a phase-extraction algorithm based on empirical mode decomposition and Hilbert transformation. The method can effectively eliminate the influence of the optical frequency scanning nonlinearity. The validity and stability of the method have been verified through simulations and experiments. Moreover, the single-cycle relative error of the phase between adjacent peaks and the standard deviation of the measurement system improved to 0.6% and 0.7 μm, respectively, with a 5 MHz sampling rate.

Frequency scanning interferometry (FSI) with a single external cavity diode laser (ECDL) and time-invariant Kalman filtering is an effective technique for measuring the distance of a dynamic target. However, due to the hysteresis of the piezoelectric ceramic transducer (PZT) actuator in the ECDL, the optical frequency sweeps of the ECDL exhibit different behaviors, depending on whether the frequency is increasing or decreasing. Consequently, the model parameters of Kalman filter appear time varying in each iteration, which produces state estimation errors with time-invariant filtering. To address this, in this paper, a time-varying Kalman filter is proposed to model the instantaneous movement of a target relative to the different optical frequency tuning durations of the ECDL. The combination of the FSI method with the time-varying Kalman filter was theoretically analyzed, and the simulation and experimental results show the proposed method greatly improves the performance of dynamic FSI measurements.

Optical frequency scanning nonlinearity seriously affects interference signal phase extraction accuracy in frequency-scanning interferometry systems using external cavity diode lasers. In this paper, an interference signal frequency tracking method using an extended Kalman filter is proposed. The interferometric phase is obtained by integrating the estimated instantaneous frequency over time. The method is independent of the laser's optical frequency scanning nonlinearity. The method is validated through simulations and experiments. The experimental results demonstrate that the relative phase extraction error in the fractional part is <1.5% with the proposed method and the standard deviation of absolute distance measurement is <2.4  μm.