Real-time Compensation Method Research Articles

Bronchoscope motion tracking using centerline-guided Gaussian mixture model in navigated bronchoscopy

Electromagnetic-based navigation bronchoscopy requires accurate and robust estimation of the bronchoscope position inside the bronchial tree. However, respiratory motion, coughing, patient movement, and airway deformation inflicted by bronchoscope significantly hinder the accuracy of intraoperative bronchoscopic localization. In this study, a real-time and automatic registration procedure was proposed to superimpose the current location of the bronchoscope to corresponding locations on a centerline extracted from bronchial computed tomography (CT) images. A centerline-guided Gaussian mixture model (CG-GMM) was introduced to register a bronchoscope’s position concerning extracted centerlines. A GMM was fitted to bronchoscope positions where the orientation likelihood was chosen to assign the membership probabilities of the mixture model, which led to preserving the global and local structures. The problem was formulated and solved under the expectation maximization framework, where the feature correspondence and spatial transformation are estimated iteratively. Validation was performed on a dynamic phantom with four different respiratory motions and four human real bronchoscopy (RB) datasets. Results of the experiments conducted on the bronchial phantom showed that the average positional tracking error using the proposed approach was equal to 1.98 0.98 mm that was reduced in comparison with independent electromagnetic tracking (EMT), iterative closest point (ICP), and coherent point drift (CPD) methods by 64%, 58%, and 53%, respectively. In the patient assessment part of the study, the average positional tracking error was 4.73 4.76 mm and compared to ICP, and CPD methods showed 31.4% improvement of successfully tracked frames. Our approach introduces a novel method for real-time respiratory motion compensation that provides reliable guidance during bronchoscopic interventions and, thus could increase the diagnostic yield of transbronchial biopsy.

Calibration method for the electrically tunable lens based on shape-changing polymer.

In this paper, a calibration method for the camera system with electrically tunable lens (ETL) based on shape-changing polymer (SCP) is proposed to improve the accuracy, robustness and practicality of the system. The camera model of the ETL based on SCP is proposed based on the analyses of its optical properties. The calibration strategy, including initial estimation of camera parameters and bundle adjustment is presented. To eliminate the influence of temperature on ETL in machine vision applications, a real-time temperature compensation method is proposed. The proposed method makes use of the existing calibration hardware without adding new components to the system. Both simulations and experiments are conducted to evaluate the effectiveness and accuracy of the proposed camera model and calibration method. The measurement error with the proposed calibration method is below 20 microns at high magnification, whose measurement accuracy is improved by five times than the existing method at high magnification. With the proposed calibration method for the camera system with ETL based on SCP, the calibration workload is reduced and accurate calibration at high magnification is achieved. It also benefits the development of autofocusing 3D measurement technology.

Large Dynamic Current Monitoring for UAV Steering Motor Using Twin Nonlinear Shunt

Steering motor is of vital importance in UAV’s health-monitoring system, to which its supply current is the most critical characteristic representing health statue of UAV. In order to conduct continuous measuring on the steering motor’s current of large dynamic range, in this paper, a current measurement method is therefore proposed on the basis of twin nonlinear shunt. The proposed method adopts the twin diode as the current sampling device, which not only realizes measurement range and relative constant resolution, but also ensures continuity of the measurement due to the eliminated operation of range switching. The associated diode is used to compensate the temperature of core temperature of the shunt diode, and to make the nonlinear-shunt more adaptive for the case of junction being heated under larger current. The working principle, real-time compensation method and circuit implementation of our method are discussed in detail. Experimental test results suggest that the measurement error of the proposed method is less than 4.5% when the measurement current varies between 10 mA to 10 A, maintaining the relative resolution at an almost constant level, while preventing the conventional method of frequent range switching from generating glitches. In addition to the ensured continuity, information-rich details of the current are sustained, contributing to the UAV’s health-monitoring system. The proposal can also be applied to other applications concerning large dynamic current detection, including, but not limited to, industrial control, motor control, etc.

Bipolar-Coding $\Phi$-OTDR with Interference Fading Elimination and Frequency Drift Compensation

Optical-pulse-coding (OPC) technique can break the trade-offs between key parameters of distributed fiber-optic sensing systems, therefore it has received great attention in recent years. OPC Φ-OTDR has achieved significant performance improvements over conventional Φ-OTDR; however, scan-rate, interference fading and frequency drift remain critical issues for this type of sensing systems. In this article, for the first time bipolar Golay coding Φ-OTDR with heterodyne detection is proposed and realized to address the scan-rate issue, the laser frequency drift is compensated by a novel real-time compensation method, and the interference fading is eliminated by incorporating the spectrum extraction and remix method. Theoretical analysis is described in detail, and the benefits provided by bipolar code are experimentally demonstrated in 10 km sensing range with 0.92m spatial resolution, achieving 7.1 dB SNR improvement and halving measurement time compared with unipolar code case. By addressing frequency drift and fading issues, the distributed sensing capability of OPC Φ-OTDR becomes available, at a reasonable expense of enlarged spatial resolution (6 m). It should be noted that, such a bipolar scheme can also be applied in other coding schemes, opening up more possibilities for OPC in Φ-OTDR.

Software compensation for the coupling error of a single-mode fiber coil under time-varying temperature and magnetic field

Previous studies have shown that there exists a large nonreciprocal phase error in the single-mode fiber coil of a depolarized interference fiber optic gyroscope (De-IFOG) under time-varying temperature and magnetic field, which evidently weakens its environmental adaptability. A real-time software compensation method considering the coupling effect of time-varying temperature and magnetic field is first proposed and verified experimentally. After compensation, the error of De-IFOG decreases from 50 deg / h to 6 deg / h when the magnitude of the magnetic field is 10 G and temperature uniformly increases from 10°C to 60°C with time-varying rate of 36 ° C / h. The compensation method is of great significance in De-IFOG engineering applications.

Real-time compensation of nonlinearity in heterodyne interferometers based on quadrature demodulation and extremum operation

The existing compensation methods for nonlinearity in heterodyne interferometers tend to be time-consuming, which limits their application in real time. To solve this problem, a real-time compensation method is proposed. First, dual-channel quadrature demodulation is used to transform the error signals in interference signals into the traditional three errors (direct current offsets, unequal amplitude errors, and phase nonorthogonal errors) in the demodulated signals. Second, the three errors are dynamically corrected by a simple algorithm based on the extremums extracted from the demodulated signals. To verify the effectiveness of the proposed method, experiments employing the proposed method were carried out to process simulated signals and to conduct actual displacement measurements. The results demonstrate that the nonlinearity in the heterodyne interferometer can be reduced down to a subnanometer level.

Autonomous reactive power support for smart photovoltaic inverter based on real-time grid-impedance measurements of a weak grid

A large share of renewable energy production is connected to a weak grid with significant grid impedance. The transmission impedance causes unintended flow of reactive power to grid, coupling the grid reactive power to the active power fed from the inverter. The reactive power causes transmission losses, strains the grid with reactive power requirements, and can even compromise system stability. Requirements on reactive power support were recently imposed on new photovoltaic inverters, which are often implemented with proportional power factor control or droop control for local voltage regulation. The present work proposes a method for real-time compensation of the unintended reactive power, which decouples the reactive power from the active power of a photovoltaic inverter. Based on real-time measurement of the grid impedance, the unintended reactive power is estimated and autonomously compensated in the inverter. The method removes the fluctuating reactive power component, while still permitting unrestricted manual control of the reactive power. Unlike conventional methods, the proposed method requires no prior knowledge on grid impedance values or delicate tuning. The method outperforms conventional power factor control even when the conventional method is tuned optimally with known grid inductance. The method is validated with simulations and experiments on three-phase photovoltaic inverter connected to a weak grid.

An accelerated convergence approach for real-time deformation compensation in large thin-walled parts machining

Abstract Excessive static deformations often occur during the end-milling of large thin-walled parts, which play an important role in the aerospace industry. The real-time adjustment of axial cutting depth (ACD) is often adopted to compensate deformation errors. Owing to the coupling effect between the ACD and the force induced deformation, the iterative adjustment of ACD is needed. However, it may not converge with the limited adjustment times especially in high-speed machining with large ACD. We hereby propose an approach to speed up the convergence of the ACD iterative adjustment. Firstly, the real-time full compensation process, which is commonly used in the existing real-time compensation methods, is mathematically analyzed and proved to be only first-order convergent. Then, an approach based on the secant method, which provides a higher order of convergence, is developed and introduced into the real-time compensation process for large thin-walled plate machining. Finally, the superiority and effectiveness of the proposed approach are demonstrated through an ACD iterative adjustment simulation and an experiment of cutting square pockets.

Two-color phase-stable dual-comb ranging without precise environmental sensing.

High-precision long geometrical distance measurement performs a vital role in large-scale manufacturing and future light detection and ranging (LIDAR) for tight formation. Its high precision, fast measurement rate, and large ambiguity range have traditionally made dual-comb ranging (DCR) a powerful tool for absolute distance measurement. However, DCR experiences the same issues caused by the refractive index of air as other laser-based ranging systems. The conventional method used to compensate refractive index of air is through using empirical equations by monitoring environment parameters. This real-time compensation method relies on precise sensors and cannot be easily applied to long-distance measurement. Thus, a two-color compensation method is proposed that requires only two co-propagating lights at different wavelengths, without specific identification of the refractive index of air. In this paper, the two-color method is combined with a low-noise DCR realized by a digital correction method. Mode resolved and phase-stable comb spectra are available for ranging at both two wavelengths with ~200 THz difference. The experimental result demonstrates 46 nm precision and 2.7 m ambiguity range by two-color DCR (TC-DCR) with 0.1 s coherent averaging at 1 kHz repetition rate difference. This method achieves a precision of the order of ~10-8 and an accuracy of the order of ~10-7, which is comparable to the single-color DCR results by empirical equations with environmental sensing. The proposed two-color DCR demonstrates great potential for long-distance measurement in open air.

A Current Reconstruction at Parallel Three Phase Inverters Using Two Current Sensors

In this paper, a current restoration method which can be applied to three phase parallel interleaved inverters (TPPII) using two current sensors has been proposed. In the proposed current reconstruction method, the branch current and the phase current of the two phases of the TPPII are sampled concurrently at the peak and valley of the pulse width modulation (PWM) carrier using two hall-effect sensors. Then, the phase current of each inverter is reconstructed by analyzing the sensed current with the current conduction path information according to the switch state in the peak and valley of the PWM carrier. This paper additionally analyzes the characteristics of the offset occurring in the detection process of two current sensors and it proposes a compensation method to reduce the offset on-line. In order to at once reduce the offset of the three-phase recovery current caused by the DC offset of the sensor, a coordinate conversion method and a low pass are used. To verify the performance of the proposed current recovery method and real-time offset compensation method, a simulation using PSIM software was performed, and experiments were conducted using a three phase parallel inverter composed of insulated gate bipolar transistor (IGBT) modules. In particular, the AC offset that occurred in the sampling process during the experiment was analyzed and modeled, and it was reduced by simple calculation.

Research on gravity vertical deflection on attitude of position and orientation system and compensation method

Position and Orientation System (POS) is the key sensor of remote-sensing system. It is a typically Strapdown Inertial Navigation System (SINS) and Global Navigation Satellite System (GNSS) integrated measurement system, which provides high-precision position and attitude parameters. The gravity disturbance vector is one of the main error sources of high-precision SINS. The error propagation of POS is analyzed. It shows that the vertical component of the gravity disturbance vector is introduced into the POS horizontal channel through the vertical deflections, which leads to the error of the attitude measurement of the POS. In this article, a new real-time gravity compensation method is proposed, which includes the gravity disturbance as the error states of POS Kalman filter, and the accurate gravity disturbance model is constructed by a “Block-Time Variation” Markov Model (B-TV-MM) based on high-precision gravity map, whose resolution is enhanced by a new interpolation method based on Gaussian Process Regression (GPR). A flight experiment was conducted to evaluate the efficiency of the proposed method and the results showed that the proposed method performs better compared with other real-time gravity compensation methods.

TOF相机实时高精度深度误差补偿方法

When using Time-Of-Flight(TOF) camera to obtain depth values, corner distortion and precision offset often occur. At present, the main methods to compensate depth errors are based on the techniques like error look-up table or curve fitting, which has a large amount of calculation resulting in slow compensation speed. By analyzing the depth error distribution law of TOF camera at different distances, a real-time and high-precision error compensation method was proposed. The error compensation model was simplifed by using the rotational symmetry of TOF depth image and the characteristics of error distribution. The order of magnitude of the parameters was reduced, and the accuracy and speed of compensation process were effectively improved. The proposed algorithm was applied to Kinect v2 depth sensor for depth compensation, the flatness error within the effective distance dropped to 0.63 mm, the average error dropped to 0.704 0 mm, and the single frame data compensation time was less than 90 ms. Since the algorithm compensates only based on the optical path difference, it is suitable for all TOF principle cameras. The results of experiments show that the proposed algorithm can quickly and effectively reduce the depth error of TOF camera, and is suitable for real-time, high-precision three-dimensional reconstruction of large field of view.

Real-time compensation method for robust polarimetric determination of glucose in turbid media.

Polarimetric determination of glucose is known to be strongly affected by scattering in turbid media. Other effects like fluctuations of light source emission and sample absorption also deteriorate glucose predictability. This work presents a measurement setup using a real-time data processing method to address these problems. The approach uses the frequency-dependent intensity components created when the polarization of the incident light is periodically modulated by a Faraday rotator. The efficacy of the proposed method was verified experimentally for a glucose range of 0 - 500 mg/dl. It was shown that the approach reduces the prediction errors in slightly turbid media from 35.7 mg/dl down to 1.17 mg/dl. In a similar way, the glucose predictability for fluctuating light source emission was improved from ±16.16 mg/dl to ±1 mg/dl and for varying sample absorbance from ±15.69 mg/dl to ±1.23 mg/dl, respectively. Therefore, considerable improvement of robustness and reproducibility of glucose determination was demonstrated.

Forward fiber Fourier transform spectrometer modeling and design with PZT phase modulation real-time compensation

Piezoelectric ceramic transducers (PZTs) are often applied in all-fiber Fourier transform spectrometers (FFTSs) to realize phase modulation. Combining a PZT and optical fiber features, a theoretical FFTS modeling is established. We systematically deduced the main causes of spectral errors and the factors of the instrumental resolution, then designed a new FFTS system and provided real-time compensation methods for spectral errors. We creatively employed two Mach-Zehnder interferometers by winding the sensing arms of the two on the same PZT cylinder to realize the dual optical path experiencing the same and simultaneous phase modulation. A processing circuit is designed to achieve selective sampling of the test interferogram, avoiding the spectral artifacts generated by the PZT phase discontinuities. The narrow line width of the reference spectrum is obtained at the same time for real-time calibration of spectral shift resulting from dispersion and other phase errors. By the comparison of the original interferogram and spectrum with those after compensation, the experiments validated that the system design could effectively compensate for the spectral errors caused by PZT and optical fiber physical limitations. Finally, the improved ideas are discussed if the FFTS prototype is to be applied to test a real-time gas spectrum.

A Real-Time Thermal Self-Elimination Method for Static Mode Operated Freestanding Piezoresistive Microcantilever-Based Biosensors.

Here, we provide a method and apparatus for real-time compensation of the thermal effect of single free-standing piezoresistive microcantilever-based biosensors. The sensor chip contained an on-chip fixed piezoresistor that served as a temperature sensor, and a multilayer microcantilever with an embedded piezoresistor served as a biomolecular sensor. This method employed the calibrated relationship between the resistance and the temperature of piezoresistors to eliminate the thermal effect on the sensor, including the temperature coefficient of resistance (TCR) and bimorph effect. From experimental results, the method was verified to reduce the signal of thermal effect from 25.6 μV/°C to 0.3 μV/°C, which was approximately two orders of magnitude less than that before the processing of the thermal elimination method. Furthermore, the proposed approach and system successfully demonstrated its effective real-time thermal self-elimination on biomolecular detection without any thermostat device to control the environmental temperature. This method realizes the miniaturization of an overall measurement system of the sensor, which can be used to develop portable medical devices and microarray analysis platforms.

A Real-time Gravity Compensation Method for a High-Precision Airborne Position and Orientation System based on a Gravity Map

Motion compensation is a significant part of an airborne remote sensing system. A Position and Orientation System (POS) can directly measure the motion information of an airborne remote sensing payload that can improve the quality of airborne remote sensing images. Gravity disturbance, information on which is often ignored due to being difficult to acquire in real-time, has become the main error source of POS in the development of inertial components. In this paper, a new real-time gravity compensation method is proposed, which includes the gravity disturbance as the error states of a POS Kalman filter, and an accurate gravity disturbance model is constructed using a time-varying Gaussian-Markov model based on a high-precision gravity map, whose resolution is enhanced by a new interpolation method based on Gaussian Process Regression (GPR). A flight experiment was conducted to evaluate the efficiency of the proposed method and the results showed that the proposed method performs well when compared with other real-time gravity compensation methods.

Synergistic real-time compensation of tracking and contouring errors for precise parametric curved contour following systems

The tracking and contouring errors are inevitable in real computer numerical control contour following because of the reasons such as servo delay and dynamics mismatch. In order to improve the motion accuracy, this paper proposes a synergistic real-time compensation method of tracking and contouring errors for precise parametric curve following of the computer numerical control systems. The tracking error for each individual axis is first compensated, by using the feed-drive models with the consideration of model uncertainties, to enhance the tracking performances of all axes. Further, the contouring error is estimated and compensated to improve the contour accuracy directly, where a high-precision contouring-error estimation algorithm, based on spatial circular approximation of the desired contour neighboring the actual motion position, is presented. Considering that the system structure is coupled after compensation, the stability of the coupled system is analyzed for design of the synergistic compensator. Innovative contributions of this study are that not only the contouring-error can be estimated with a high precision in real time, but also the tracking and contouring performances can be simultaneously improved although there exist modeling errors and disturbances. Simulation and experimental tests demonstrate the effectiveness and advantages of the proposed method.

Adaptive estimation and nonlinear variable gain compensation of the contouring error for precise parametric curve following

Contour following is one of the most important issues faced by many computer-numerical-control (CNC) machine tools to achieve high machining precision. This paper presents a new real-time error compensation method aiming at reducing the contouring error caused by facts such as servo lag and dynamics mismatch in parametric curved contour-following tasks. Due to the lack of high-precision contouring-error estimation method for free-form parametric curved toolpath, the error can hardly be compensated effectively. Therefore, an adaptive accurate contouring-error estimation algorithm is proposed first, where a tangential-error backstepping method based on Taylor’s expansion is developed to rapidly find the closest point on the parametric curve to the actual motion position. On this foundation, the contouring error is compensated using a proposed nonlinear variable-gain compensation method, where the compensation gain is obtained according to not only the contouring-error magnitude but also its direction variation. The stability of the system after compensation is analyzed afterwards according to the Jury stability criterion. By design of the compensator in accordance with the presented contouring-error compensation method as well as the stability analyzation result, the balance between the response speed and the contour control stability can be effectively made. Experimental tests demonstrate the feasibility of the presented methods in both contouring-error estimation and contour-accuracy improvement. Contributions of this research are significant for enhancing the contour-following performance of the CNC machine tools.

Analysis and compensation of synchronous measurement error for multi-channel laser interferometer

Dual-frequency laser interferometer has been widely used in precision motion system as a displacement sensor, to achieve nanoscale positioning or synchronization accuracy. In a multi-channel laser interferometer synchronous measurement system, signal delays are different in the different channels, which will cause asynchronous measurement, and then lead to measurement error, synchronous measurement error (SME). Based on signal delay analysis of the measurement system, this paper presents a multi-channel SME framework for synchronous measurement, and establishes the model between SME and motion velocity. Further, a real-time compensation method for SME is proposed. This method has been verified in a self-developed laser interferometer signal processing board (SPB). The experiment result showed that, using this compensation method, at a motion velocity 0.89 m s−1, the max SME between two measuring channels in the SPB is 1.1 nm. This method is more easily implemented and applied to engineering than the method of directly testing smaller signal delay.

Real-time phase delay compensation of PGC demodulation in sinusoidal phase-modulation interferometer for nanometer displacement measurement.

As the phase delay between the carrier component of the detected interference signal and the carrier has adverse effect for phase generated carrier (PGC) demodulation, it is essential to compensate the phase delay to improve the accuracy of precision displacement measurement in sinusoidal phase-modulation interferometer (SPMI). In this paper, a real-time phase delay compensation method is proposed by regulating a compensating phase introduced to the carrier to maximize the output of the low pass filter so as to make the carrier synchronize with the interference signal. The influence of phase delay for PGC demodulation is analyzed and the method for real-time phase delay compensation is described in detail. The simulation of the method was performed to verify the validity of the phase delay compensation algorithm. A SPMI using an EOM was constructed and several comparative experiments were carried out to demonstrate the feasibility of the proposed method. The experimental results show that the phase delay can be compensated accurately in real time, and nanometer accuracy is achieved for precision displacement measurement.