Improved calibration method for displacement transformation coefficient in optical and visual measurements

Optical and visual measurement technology is used widely in fields that involve geometric measurements,and among such technology are laser and vision-based displacement measuring modules(LVDMMs).The displacement transformation coefficient(DTC)of an LVDMM changes with the coordinates in the camera image coordinate system during the displacement measuring process,and these changes affect the displacement measurement accuracy of LVDMMs in the full field of view(FFOV).To give LVDMMs higher accuracy in the FFOV and make them adaptable to widely varying measurement demands,a new calibration method is proposed to improve the displacement measurement accuracy of LVDMMs in the FFOV.First,an image coordinate system,a pixel measurement coordinate system,and a displacement measurement coordinate system are established on the laser receiving screen of the LVDMM.In addition,marker spots in the FFOV are selected,and the DTCs at the marker spots are obtained from calibration experiments.Also,a fitting method based on locally weighted scatterplot smoothing(LOWESS)is selected,and with this fitting method the distribution functions of the DTCs in the FFOV are obtained based on the DTCs at the marker spots.Finally,the calibrated distribution functions of the DTCs are applied to the LVDMM,and experiments conducted to verify the displacement measurement accuracies are reported.The results show that the FFOV measurement accuracies for horizontal and vertical displacements are better than±15μm and±19μm,respectively,and that for oblique displacement is better than±24μm.Compared with the traditional calibration method,the displacement measurement error in the FFOV is now 90%smaller.This research on an improved calibration method has certain significance for improving the measurement accuracy of LVDMMs in the FFOV,and it provides a new method and idea for other vision-based fields in which camera parameters must be calibrated.

Practical calibration method for instantaneous polarization radar systems utilizing a metal sphere

A practical calibration method is proposed for instantaneous polarization radar systems.The method only needs one measurement by using a metal sphere.The distortions of system and the actual polarization scattering matrix(PSM)of target can be obtained.First,an instantaneous polarization radar system is presented.The system can obtain PSM by a single pulse echo.The dual-polarization antenna can transmit and receive two orthogonal polarization waves.The multilayer micro-strip patch antenna is adopted for this kind of radar system.Second,based on the multi-port network theory,the operation and system errors of instantaneous polarization radar system are analyzed.By making assumption on the cross-talk factors of antenna,distortion matrices of R and Tare derived.Finally,the calibration method based on instantaneous polarization measurement is introduced.Simulation results show the performance of this calibration method.The values of calibrated PSM are in agreement with the actual ones after calibration.

Study on the Drift Calibration Method and Device for the Tin Oxide pH Electrode

Drift phenomenon has been known as the drawback of sensors and causes inaccuracy on the long-term measurement. In general,there are two methods to reduce the drift problem.One is to tune the parameters of the fabrication process to improve the properties of the front-ended device.Another is to compensate the drift phenomenon by adding extra drift compensation circuit or software in the back-ended readout circuit.In this study,a drift calibration method for the potentiometric sensor was presented and the drift calibration method was performed by using the circuit.According to experimental results,the drift phenomenon of the SnO_2 pH electrode was reduced by the drift calibration device.

A method to determine the bonded-particle model parameters for simulation of ores

The bonded-particle model(BPM)is commonly used in the numerical analysis of ore samples.To improve the accuracy of simulating the mechanical process of ore process of ore crushing in a crusher,the parameters of the BPM for the ore must be calibrated.In this study,a calibration method was proposed for the scientific determination of the parameters of the BPM for ore undergoing uniaxial compression.First,physical tests and simulations were conducted to determine the mechanical response(uniaxial compressive strength and macroscopic stiffness)of ore during uniaxial compression.Then,the sensitivity of the mechanical response to the values of microscopic parameters was tested using a Plackett-Burman design.Next,the microscopic parameters with the greatest impact on the response were identified,and the range of parameters that met the target response was determined using a steepest ascent design;Second,a second-order model of the mechanical response was established using the sensitive parameters by combining a Box-Behnken design with response surface methodology to obtain the optimal BPM parameters.Simulation tests showed that the normal stiffness per unit area,critical shear stress,and bonded disk radius had significant effects on the uniaxial compressive strength(UCS)and macroscopic stiffness(MS).To verify the validity of the proposed calibration method,laboratory tests were conducted.The consistency of the simulation results with experimental results indicated that response surface methodology with the Plackett-Burman design,steepest ascent design,and Box-Behnken design can be an effective method for calibrating the BPM of ores.

Study on Calibration of L-band Radar by a Drone

A new calibration method of L-band radar accuracy using a rotary-wing drone equipped with"GPS"satellite positioning system was proposed.The L-band radar calibration system scheme based on this method was designed.The theoretical basis required for system realization was studied,and the system calibration method was given.The calibration results referred to the domestic new generation weather radar antenna beam pointing calibration technical indicator(≤0.3°),and its accuracy met relevant business requirement.It show that this method can easily and quickly complete the radar system calibration.Compared with the traditional radar calibration method,it is more convenient,less affected by surrounding environment,and has low requirements on the weather.

Calibration method to improve the accuracy of THz imaging and spectroscopy in reflection geometry

We introduce a novel method to accurately extract the optical parameters in terahertz reflection imaging. Our method builds on standard self-referencing methods using the reflected signal from the bottom of the imaging window material to further compensate for time-dependent system fluctuations and position-dependent variation in the window thickness. Our proposed method not only improves the accuracy, but also simplifies the imaging procedure and reduces measurement times.

Method for in situ calibration of multiple feedback interferometers

A method is presented for in situ resolution calibration of multiple feedback interferometers(MFIs)using two lasers with di?erent feedback levels simultaneously.The laser with weak optical feedback level generates half-wavelength optical fringes,whereas the laser with strong multiple feedback level generates optical nanofringes.By using this method,the number of displaced optical nano-fringes can be easily counted,and the resolution of the MFIs can be accurately determined.The integrated MFIs can be used to measure displacements and calibrate other displacement sensors.

Accelerometer Bias and Star Sensor Installation Error Joint Calibration for the SINS/CNS Integrated Navigation System Using Attitude Maneuver

The integrated strap-down inertial nav igation system/olelestial navigation system(SINS/CNS)i an important autonomous navigation method with efective concealment and high predision.Both accelerometer biss and star ensor installation error ame important factors that aflect the performanoe of this mavigation system,which needl to be calibratexd and compensatedl.A new acelerometer bias and star sensor installation error joint calibration method for the SINS/CNS integrated navigation system i propoeed.In this newly propoeed method,the installation error of star sensor is augmented to the state vector,and the star vector,nadir angle,horkzontal poeition error and velbcity error ame ueed a8 measurementa to calbrate the two errors mentioned above.Simulations show that both accelerometer bias and star sensor installation enror an be calibratedl efectively.

Time-Modulated Arrays:A Four-Dimensional Antenna Array Controlled by Switches

With the rapid development of modern electronic technologies,antenna arrays typically operate in very complex electromagnetic environments.However,owing to the various errors such as systematic errors and random errors,conventional antenna arrays have relatively high sidelobes.Time modulated arrays(TMAs),also known as four-dimensional(4-D)antenna arrays,introduce time as an additional dimension for generating ultra-low sidelobes at fundamental component and realizing real-time beam scanning by harmonic components.Recently,the harmonic components can also be developed for various new applications including wireless communications and radar systems.In this review,we introduce comprehensively the fundamental methodologies and recent applications of TMAs.This aims to stimulate continuing efforts for the understanding of TMAs and explore their applications in various aspects.The methods mentioned in this review include three aspects:sideband radiation suppression,power efficiency of TMAs,and applications of harmonic components.These methods either improve the existing TMAs or promote the practical applications of TMAs.First,to suppress the sideband radiation,a method using non-uniform periodical modulation is introduced.The proposed method has an advantage of low computation and can be easily used for synthesizing a real-time radiation pattern according to the environmental need.Next,a TMA structure using reconfigurable power dividers/combiner is introduced to improve the power efficiency of feeding network.Finally,three applications of harmonic component including direction finding,calibration method,and space division multiple access are separately introduced to illustrate the development potential of TMAs.