Conventional Calibration Methods Research Articles

Fast Thermal Calibration of Low-Grade Inertial Sensors and Inertial Measurement Units

The errors of low-cost inertial sensors, especially Micro-Electro Mechanical Systems (MEMS) ones, are highly dependent on environmental conditions such as the temperature. Thus, there is a need for the development of accurate and reliable thermal compensation models to reduce the impact of such thermal drift of the sensors. Since the conventional thermal calibration methods are typically time-consuming and costly, an efficient thermal calibration method to investigate the thermal drift of a full set of gyroscope and accelerometer errors (i.e., biases, scale factor errors and non-orthogonalities) over the entire temperature range in a few hours is proposed. The proposed method uses the idea of the Ramp method, which removes the time-consuming process of stabilizing the sensor temperature, and addresses its inherent problems with several improvements. We change the temperature linearly for a complete cycle and take a balanced strategy by making comprehensive use of the sensor measurements during both heating and cooling processes. Besides, an efficient 8-step rotate-and-static scheme is designed to further improve the calibration accuracy and efficiency. Real calibration tests showed that the proposed method is suitable for low-grade IMUs and for both lab and factory calibration due to its efficiency and sufficient accuracy.

W-band active loads and switching front-end MMICs for radiometer calibration

A millimeter-wave monolithic integrated circuit consisting of a W-band (75–100 GHz) single-pole-five-throw (SP5T) switch and multiple internal active and passive loads for radiometer calibration was designed and manufactured in a low noise 50 nm GaAs metamorphic high electron mobility transistor technology. This highly compact and integrated front-end device for radiometer systems is capable of ultra fast switching between two identical input ports (e.g. for polarimetric applications) and three internal calibration references. It allows an accurate multi-load calibration with noise temperatures between 220 and 1750 K at the output of the device. Compared to conventional calibration methods this marks a substantial advantage in terms of size, mass, power consumption, complexity, and repetition rate.

Multiple Pivot loading 방법을 이용한 액체 환경에서의 수평방향 힘 교정

Quantifying the nanoscale force between the atomic force microscopy (AFM) probe of a force-sensing cantilever and the sample is one of the challenges faced by AFM researchers. The normal force calibration is straightforward; however, the lateral force is complicated due to the twisting motion of the cantilever. Force measurement in a liquid environment is often needed for biological applications; however, calibrating the force of the AFM probes for those applications is more difficult owing to the limitations of conventional calibration methods. In this work, an accurate nondestructive lateral force calibration method using multiple pivot loading was proposed for liquid environment. The torque sensitivity at the location of the integrated probe was extrapolated based on accurately measured torque sensitivities across the cantilever width along a few cantilever lengths. The uncertainty of the torque sensitivity at the location of the integrated tip was about 13%, which is significantly smaller than those for other calibration methods in a liquid environment.

Identification Method of Sensor Directions and Sensitivities in Multi-Axis Accelerometer (Actual Measurement of Direction Tensor and Sensitivity Tensor)

An accelerometer generally has direction gaps between the package and the actual sensors. Conventional accelerometer calibration methods, e.g., ISO standard, do not consider this direction gap. This study proposes a new calibration method. The method uses a new examination system with a parallel linkage exciter mechanism. The exciter rotates a target accelerometer in a uniform circular motion, and the posture of the accelerometer is kept constant against external coordinates. The required torque for the rotation is small and constant because the rotation components are balanced with counterweights. Therefore, the exciter applies a stable sine wave acceleration to the accelerometer. This method contributes not only to the accuracy of input acceleration but also to the removal of offset noise. In addition, the input acceleration is calculated only by one differential computation, whereas an ordinary mechanism requires a second order differential. From the accelerometer output, a plane including the actual sensor direction is detected by the sine curve profile. The direction of the actual sensor is the line of intersection of two measured planes. For a 3-axis accelerometer, measurement 2 times is enough to determine all actual sensor directions and sensitivities with this method (measurement one time is enough for a 2-axis accelerometer). Actual sensor directions and sensitivities are experimentally examined. The result is consistent with the data sheet of the test accelerometer.11. This paper is the full translation from the transactions of JSME, Series C, Vol.78, No.786, pp. 499-507, 2012.

Projector calibration with error surface compensation method in the structured light three-dimensional measurement system

In the structured light three-dimensional measurement system, calibration is the key to the measurement accuracy; however, conventional calibration methods for the projector are either too complex or inaccurate. Therefore, we propose a simple and accurate method to calibrate the projector. In this method, the calibration points in the camera image plane can be mapped to the projector according the homography of the planar projection. In addition, an error surface compensation method is developed to minimize mapping errors caused by lens distortion of the camera and projector. As a result, the projector can be calibrated with the same method as the camera. Experiments are conducted to verify the effectiveness of the proposed method.

Calibration Method for Stereovision Measurement of High-Temperature Components Using Two Infrared Cameras

The infrared vision measurement method has some advantages over visible vision in the measurement of high-temperature components. Infrared imaging is based on different imaging principles, however, making it unreasonable to adopt a conventional visiblelight camera calibration method directly. The present study proposes a dual infrared-camera calibration program in which we use the infrared imaging principle to measure high-temperature components threedimensionally. We use two ceramic balls as calibration targets against the background of an external hightemperature radiation source. Multiple feature points are generated from the precise movement of these targets. In order to improve the accuracy of the calibration method, we took the following approaches: A highly accurate edge-detection algorithm is realized by using a fuzzy neural network that is self-learning, self-adaptive, and utilizes fuzzy processing. We thus achieve a low signal-to-noise ratio and low contrast in infrared images. The distance between these two ceramic targets is used as a calibration reference to further reduce the temperature effect and to improve calibration accuracy and efficiency. The calibration results we got are an average residual error of 6.4134 µm and a variance of 2.9205 µm.

DC offset calibration method for zero-IF receiver removing the PGA-gain-correlated offset residue

This paper presents a novel DC offset calibration method for the zero-IF (intermediate frequency) receiver that removes the PGA-gain-correlated offset residue. The conventional calibration method usually uses the classic input/output referred offset model, in which the receiver IF programmable gain amplifiers (PGAs) have offset sources that varies a lot with different gain settings. Consequently, the conventional calibration method needs to generate the calibration code at each gain step and requires a huge look up table (LUT) to store the calibration values. This paper presents a new DC offset model which is gain non-correlated, by analyzing two types of commonly used PGA. Based on the new model, a LUT-free single-step DC offset calibration method in together with the implementation circuit is designed. The proposed method has been verified on a practical zero-IF receiver circuit in a standard 0.18μm CMOS technology through the Monte Carlo (MC) simulation. The simulation results show that the receiver IF output offset residue after calibration using the proposed method is reduced to below 12mV, in contrast to 200mV by the conventional method.

An accurate calibration method for a camera with telecentric lenses

It is very important to achieve an accurate calibration to obtain high measurement accuracy for a telecentric imaging system. However, the conventional camera calibration methods typically based on a pinhole model are not suitable for telecentric lenses due to the unique behavior of orthographic projection of telecentric lenses. In this paper, we propose a new method to accurately calibrate the telecentric imaging system. An analytical camera model for telecentric lenses is presented with considering the major sources of lens distortions. Based on this model, a two-step calibration procedure is described for the telecentric imaging system. We use a camera with a telecentric lens to verify our model and study the impacts of different distortion models for properly characterizing the distortion of telecentric lens. The experimental results show the maximum distortion of the system reduces 26 times by the presented calibration technology.

Comparison Among Cross, Onboard and Vicarious Calibrations for Terra/ASTER/VNIR

Comparative study on radiometric calibration methods among onboard, cross and vicarious calibration for visible to near infrared radiometers onboard satellites is conducted. The data sources of the aforementioned three calibration methods are different and independent. Therefore, it may say that the reliable Radiometric Calibration Accuracy: RCC would be the RCC which are resemble each other two of three RCCs. As experimental results, it is found that vicarious and cross calibration are reliable than onboard calibration. Also vicarious calibration based cross calibration method is proposed here. The proposed cross calibration method should be superior to the conventional cross calibration method based on band-to-band data comparison. Through experiments, it is also found that the proposed cross calibration is better than the conventional cross calibration. The radiometric calibration accuracy of the conventional cross calibration method can be evaluated by using the proposed cross calibration method.

A Method on Monocular Vision of Camera for Spatial Position

In this paper, a method on monocular vision for spatial position is presented. The geometric model of digital camera is built and decomposed to intrinsic and extrinsic parameter matrixes under a certain assumption. Firstly, the intrinsic parameter matrix of camera is determined. Then, the extrinsic parameter matrix is solved according to the information of image. The edge detection operators are worked and in order to detect the accuracy of this method, the point of some feature points are obtained by using the principle of least squares. Compared with the conventional calibration method, this method is simple, fast and robust.

Improving data stability and prediction accuracy in laser-induced breakdown spectroscopy by utilizing a combined atomic and ionic line algorithm

Improving data quality is important for accurate quantitative analysis in laser-induced breakdown spectroscopy for time and spatial integrated spectra. Based on the characteristics of atomic and ionic lines under various plasma conditions, an algorithm is proposed to reduce the signal fluctuation by combining an atomic line and an ionic line of an element. Using 29 brass alloy samples, the algorithm is verified by comparing the relative standard deviations of the intensities of two copper lines, Cu(I) 406.264 nm and Cu(II) 217.941 nm, to that of their combined intensity. The noticeable improvement suggests that the proposed algorithm can overcome the signal fluctuation caused by the varying plasma temperature and electron density. Furthermore, using the conventional linear calibration method, the relative standard deviation is reduced from 2.93% (Cu(I) 406.264 nm) and 2.13% (Cu(II) 217.941 nm) to 1.68% (combined intensity), and the root mean square error of prediction is significantly reduced from 2.24% (Cu(I) 406.264 nm) and 2.43% (Cu(II) 217.941 nm) to 1.40% (combined intensity).

715 GAを用いたレーザーレンジファインダキャリブレーション(OS7 オーガナイズドセッション《精密/微細加工と評価》)

A triangulation-based laser rangefinder is able to achieve a favorable balance between measurement accuracy and measurement time. However, conventional triangulation-based rangefinders are known to be difficult to apply to the 3-D shape measurement of specular objects with shiny surfaces. We previously proposed a laser rangefinder applicable to specular object, which consist of laser projector, lens, half-mirror, and two image sensors. It is shown that the accuracy of the rangefinder is sensitive to misalignment of these parts, however, conventional camera calibration methods cannot correct the misalignment of this rangefinder. To overcome this problem, we proposed a novel laser rangefinder calibration method by using of Genetic Algorithm.

Terahertz time-domain spectroscopic ellipsometry: instrumentation and calibration

We present a new instrumentation and calibration procedure for terahertz time-domain spectroscopic ellipsometry (THz-TDSE) that is a newly established characterization technique. The experimental setup is capable of providing arbitrary angle of incidence in the range of 15°-85° in the reflection geometry, and with no need for realignment. The setup is also configurable easily into transmission geometry. For this setup, we successfully used hollow core photonic band gap fiber with no pre-chirping in order to deliver a femtosecond laser into a THz photoconductive antenna detector, which is the first demonstration of this kind. The proposed calibration scheme can compensate for the non-ideality of the polarization response of the THz photoconductive antenna detector as well as that of wire grid polarizers used in the setup. In the calibration scheme, the ellipsometric parameters are obtained through a regression algorithm which we have adapted from the conventional regression calibration method developed for rotating element optical ellipsometers, and used here for the first time for THz-TDSE. As a proof-of-principle demonstration, results are presented for a high resistivity silicon substrate as well as an opaque Si substrate with a high phosphorus concentration. We also demonstrate the capacity to measure a few micron thick grown thermal oxide on top of Si. Each sample was characterized by THz-TDSE in reflection geometry with different angle of incidence.

A New In-Camera Imaging Model for Color Computer Vision and Its Application

We present a study of in-camera image processing through an extensive analysis of more than 10,000 images from over 30 cameras. The goal of this work is to investigate if image values can be transformed to physically meaningful values, and if so, when and how this can be done. From our analysis, we found a major limitation of the imaging model employed in conventional radiometric calibration methods and propose a new in-camera imaging model that fits well with today's cameras. With the new model, we present associated calibration procedures that allow us to convert sRGB images back to their original CCD RAW responses in a manner that is significantly more accurate than any existing methods. Additionally, we show how this new imaging model can be used to build an image correction application that converts an sRGB input image captured with the wrong camera settings to an sRGB output image that would have been recorded under the correct settings of a specific camera.

A simple calibration method for structured light-based 3D profile measurement

Structured light is commonly applied to various 3D surface profile measurements because of its nature of low cost and high speed. The existing structured light-based reconstruction model and calibration can be classified as analytical and empirical methods, among which the empirical methods are often used since it is pixel-wise method. However, the existing empirical matching difference-height models are oversimplified and the empirical calibration methods are cumbersome and time-consuming. Therefore, two contributions of this paper are: first, we derive a general matching difference-height model with high consistence and resolution, the proposed model is independent of hardware configuration; second, a multi-sphere calibration strategy is proposed to simplify and accelerate the calibration procedure by a flat board with four balls. Some experiments are carried out to evaluate the proposed methods. The experimental results demonstrate that matching difference-height model improves the resolution and consistency by 3% and 13% in comparison with the traditional models; while, the proposed calibration duration is reduced to 27% of the conventional plane-translation calibration method.

Post-Packaged Measurement of MEMS Gap, Displacement, Force, Stiffness, Mass, Damping, and Quality Factor

What is presented: We present a practical MEMS metrology technology that can be used to extract system stiffness, mass, damping, and excitation force after a MEMS is packaged. Presently the technology applies to planar MEMS with comb drives. Our method is quick, accurate, and precise. Why important: Our technology will likely be important for manufacture, accuracy, and controllability. During manufacture, MEMS metrology can be 30% to 40% of the cost. This high cost is due to factory testing tools that are impractical and not optimized for batch fabrication. The tools often apply an external disturbance that the MEMS are electronically tuned to. Accuracy is a critical problem area in MEMS. Often MEMS are more sensitive and precise than the tools used to calibrate them. And there are no ASTM standards in MEMS for measuring stiffness, mass, damping, and force. Since there is a lack of standards, high cost in metrology, and low return on measurement due to large uncertainties, it has been difficult for manufacturers and their customers to agree on calibration technologies. Moreover, calibration in controlled laboratory conditions may not be consistent with conduction due to harsh environmental changes or long-term dormancy. Conventional calibration methods often treat MEMS as a black box, where numerous parameters remain uncharacterized. Without complete characterization, a complete understanding of what is being sensed is unlikely. However, by measuring the stiffness, mass, damping, and excitation forces on-chip, MEMS can become self-calibrating and offer more complete analysis of what is being sensed. What is different: Our method consists of using on-chip or off-the-shelf electronics to measure changes in capacitance to measure geometry, displacement, stiffness, and comb drive force. Upon measuring stiffness, mass is determined by velocity resonant frequency. The benefit of using changes in capacitance is that our technology is independent of meter accuracy; that is, it is the precision of the meter that matters. E.g. Zeptofarad precision has been realized by a few groups. Such an independence from absolute measurements allows our technology to be repeatable between different laboratories, where parasitics will likely differ. Results: We validate our electro-metrology technology for geometry, displacement, stiffness, and force. Our results of geometry compares favorably against geometry measured by a scanning electron microscope by 2 orders of magnitude. We validate displacement by measuring the distance traveled between a pair fabricated displacement stops. Stiffness and force are simi-validated by applying an identical (but unknown) AFM-cantilever force to two different MEMS which are each calibrated using our method. Although such a method does not directly provide a traceable measurement of force, it does imply the possibility of developing a standard of measure because the same value of force is obtained across different devices.

Interference standard and oxide ion detection as strategies to determine phosphorus and sulfur in fuel samples by inductively coupled plasma quadrupole mass spectrometry

Due to their high ionization energies and severe spectral interferences, P and S are challenging elements in inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). An alternative to improve sensitivity is to monitor P and S oxide and hydroxide species which are easily formed under cool plasma conditions. To improve accuracy, an interesting approach is the interference standard (IFS) method. Similar to internal standardization, the IFS method is based on the idea that interfering polyatomic ions and some Ar species (IFS) present similar behaviors in the plasma. Thus, by applying a conventional external calibration method and using the analytical–IFS signal ratio, one can minimize the contribution of the interfering ion to the analytical signal and improve accuracy. In this work, plasma operating conditions are adjusted to maximize the formation of 31P16O+, 32S16O+ and 32S16OH+. Under the optimal conditions and using the 36ArH+ as an IFS probe, limits of detection as low as 5 and 600 μg l−1 are obtained for P and S determined at m/z 47 and 49, respectively. The efficiency of the IFS method in reducing interferences, e.g.30Si16OH+ on 31P16O+, and 31P16OH+ on 32S16O+, is also evaluated. Accuracy is significantly improved in lubricating oil, diesel and biodiesel analyses. No significant differences are observed between the reference values and the ones obtained with the 36ArH+ IFS probe at a 95% confidence level. The 36Ar+ and 38Ar+ IFS probes are also efficient in most determinations.

Calibration of an Accelerometer

Conventional calibration method of an accelerometer does not take account of the direction gap between the package and the internal sensors. The gap causes sensitivity error and crosstalk of other axis acceleration. These errors prevent to calculate accurate input acceleration. This study proposes a new calibration method which provides actual sensor directions and individual sensitivities.

New self-calibration approach to space robots based on hand-eye vision

To overcome the influence of on-orbit extreme temperature environment on the tool pose (position and orientation) accuracy of a space robot, a new self-calibration method based on a measurement camera (hand-eye vision) attached to its end-effector was presented. Using the relative pose errors between the two adjacent calibration positions of the space robot, the cost function of the calibration was built, which was different from the conventional calibration method. The particle swarm optimization algorithm (PSO) was used to optimize the function to realize the geometrical parameter identification of the space robot. The above calibration method was carried out through self-calibration simulation of a six-DOF space robot whose end-effector was equipped with hand-eye vision. The results showed that after calibration there was a significant improvement of tool pose accuracy in a set of independent reference positions, which verified the feasibility of the method. At the same time, because it was unnecessary for this method to know the transformation matrix from the robot base to the calibration plate, it reduced the complexity of calibration model and shortened the error propagation chain, which benefited to improve the calibration accuracy.

Improved calibration method for SDINS considering body-frame drift

A calibration method for a strap-down inertial navigation system (SDINS) is presented here. The body-frame drift induced by the variation of the accelerometer sensing axe due to temperature changes is an important source of navigation error not considered in conventional calibration methods. In this paper, we propose an advanced calibration method that can compensate for SDINS error sources including not only bias, scale factor, and misalignment but also the body-frame drift by utilizing a 2-axis turntable. The body-frame drift is estimated using horizontal accelerometer measurements during a calibration procedure. Simulation results show that the body-frame drift behaves like an additional gyro bias error and that the proposed calibration technique can significantly improve pure navigation performance by removing the effect of body-frame drift.