Probe Error Research Articles

Method of compensating for instrumental uncertainty in measurements using a coordinate measuring ARM

Due to the influence of dynamic factors in various measurement configurations, the degree of uncertainty in measurements using a Coordinate Measuring Arm (CMA) is directly related to the measurement configuration. However, existing models for compensating CMA errors do not account dynamic factors, which impose certain limits for improving the accuracy of CMAs. To solve this issue, a method for residual error correction based on a polynomial model for single-point measurements was proposed. The influence of the CMA configuration on the residual probe error was analyzed. To enhance accuracy, a polynomial model has been developed by studying the relationship between the rotation angles of the CMA's moving elements and the probe coordinates in a cylindrical coordinate system. Experimental results demonstrate that the residual error correction method significantly compensates for instrumental uncertainty, greatly improving the accuracy of measurements using CMAs. Keywords: coordinate measuring arm, measurement error, coordinate measurements, calculation method, single-point residual correction, compensation.

Touch-trigger probe error compensation for nonvertical on-machine measurement of freeform surface workpieces

Touch-trigger probe error compensation for nonvertical on-machine measurement of freeform surface workpieces

Contact on-machine measurement probe error correction method for optical aspheric surface ultraprecision machining

Optical aspheric ultraprecision machining requires nanometer-scale on-machine measurement (OMM) techniques, and small probe errors in the contact OMM process can seriously affect the OMM accuracy, thereby reducing machining accuracy. Thus, a master ball-based probe radius error and probe profile error correction method is proposed to analyze the effects of probe radius error and probe profile error on OMM results while ensuring accurate probe alignment to establish an identification and correction model for probe radius error and probe profile error. OMM probe error correction measurement and error compensation machining experiments were conducted to verify the effectiveness of the probe error correction method. After the probe profile error correction measurement, the probe measurement error was changed from 0.436 μm to 0.023 μm. Compared with the uncorrected probe error and the probe radius error correction compensation machining results, the accuracy of the compensation machining after the probe profile error correction compensation was improved by 43 % and 41 %, respectively. Results show that this OMM system probe error correction method is effective in improving OMM accuracy.

Comparison between Air Temperature and Land Surface Temperature for the City of São Paulo, Brazil

This study aims to identify the relationship between changes in temperature regarding urbanization processes and seasonality in the city of São Paulo, located in the Tropic of Capricorn. The land surface temperature (LST) results were compared to official weather stations measurements, identifying in the spring–summer period 65.5% to 86.2% accuracy, while in the autumn–winter period, the results ranged from 58.6% to 93.1% accuracy, when considering the standard deviation and the temperature probe error. The mean MAE and mean RMSE range from 1.2 to 1.9 °C, with 83.0% of the values being ≤2.7 °C, and the coefficient of determination values are R = 0.81 in spring–summer and R = 0.82 in autumn–winter. Great thermal amplitude was estimated in the spring–summer season, with a difference in LST of the built-up space and rural area ranging from 5.8 and 11.5 °C, while in the autumn–winter season, the LST is more distributed through the city, with differences ranging from 4.4 to 8.5 °C. In addition, the current study suggests remote sensing as a reliable, cheap, and practical methodology to assist climate in order to support public policies and decision-making actions regarding environmental and urban planning.

The share of the probe errors in on-machine measurements

The influence of the errors of touch-trigger probes for machine tools on the result of the basic measuring tasks performed by CNC was examined. The goals of the analysis were, first, to estimate an uncompensated value of the error which occurs during different qualification cycles, and second, to determine the influence of the qualification on the measurement of features such as distance, a circle and the position of corner. The investigation was based on the results of research on a few probes, for which the values of the triggering radius in the form of spatial characteristic in a laboratory were determined. The obtained results show that although the qualification cycle reduces the influence of the probe error on the measurement result and increasing the number of qualification points improves the compensation conditions, this error is not completely eliminated, and its value can reach as much as several tens of micrometres.

Determination of probe non-linearity and error due to measurement position for direct measurement type of gauge block comparator and its measurement uncertainty

The non-linearity of probes is one of the important components in gauge block calibration by the mechanical comparative method of two gauges blocks at the same nominal length. However, an advanced method for gauge block calibration is a mechanical direct measurement method of two gauge blocks showing the greatest difference in nominal length of 25 mm. This method uses a special probe based on the interferential scanning principle to produce the signals to measure the displacement. In this paper, non-linearity and error due to measurement position were investigated as they related to the accuracy of measurement results. The differences in central length of pairs of standard gauge blocks made of steel were measured by optical interferometry with the measurement uncertainty (k=2) 23 nm. Length in the range of 5 μm to 25 mm was used in the experiment. Non-linearity of the probe was evaluated by the simple linear regression model. Various factors such as origin setting point, temperature, and vibration have been analysed. In the preliminary experiment, the non-linearity, position error, repeatability and retrace error over the measuring range 25 mm are 13 nm, -18 nm, 15 nm, and 10 nm respectively. The standard uncertainty of direct measurement type caused by non-linearity is 4 nm.

The level of representation of irrelevant stimuli\u2014Distractor\u2013response binding within and between the senses

Binding theories assume that features of stimuli and executed responses can be integrated together in one event file (Hommel, Visual Cognition, 5, 183–216, 1998; Hommel, Cognitive Sciences, 8, 494–500, 2004). Every reencounter with one or more of the stored features leads to an automatic retrieval of the previously constructed event file and hence of the response—even the repetition of a task-irrelevant distractor stimulus can retrieve a previously encoded response. This so-called distractor–response binding effect is typically investigated using a sequential prime-probe design that allows the orthogonal variation of response relation (response repetition vs. resporrevertnse change) and distractor relation (distractor repetition vs. distractor change), while probe response times and error rates are measured as dependent variable. Previous research has shown that task-relevant stimuli can be represented at different levels (e.g., perceptual and conceptual; see Henson et al., Trends in Cognitive Sciences, 18, 376–384, 2014), yet it is not clear at which level of representation distractor stimuli are processed. In the present study, we focused on the level of representation of response-irrelevant distractor stimuli. To this end, a crossmodal distractor–response binding paradigm was used that enables the differentiation between the perceptual and conceptual representation of the distractor by allowing the systematic repetition and change of conceptual distractor features independent of perceptual repetitions. The results suggest that the repetition of perceptual distractor features is indispensable for the initiation of the retrieval process while the sole repetition of conceptual distractor features is not sufficient to start the retrieval process.

Measurement of five-degrees-of-freedom spindle error motion using multi probe error separation

Herein, a precision measurement method is proposed to evaluate the radial, axial, and tilt error motions of rotating devices such as precision spindles. To improve the accuracy of the estimated multiple-degree-of-freedom error motion components, form error signals in the runout signals are separated and precompensated for before the calculation of the five-degrees-of-freedom error motion components. Fourier model-based multi probe error separation (MPES) techniques, which can prevent the occurrence of harmonic distortions, are applied to separate the form error signals. A three-probe method is applied to layers on the side surface of the cylindrical artifact, and a modified two-probe method is developed and applied to the upper surface. The radial, tilt, and axial error motions are calculated using the runout signals that do not contain the separated form error signals. The measurement system uses eight capacitive probes to detect the runout signals of the cylindrical artifact mounted at the center of the rotating device. To compare the proposed method with the five-probe-based conventional measuring method, an evaluation test simulation is conducted repeatedly five times. Results indicate that the proposed MPES method calculated the uncertainty using the deviation between the computed results from the existing and novel methods; additionally, the input signal in terms of the radial, tilt (layers 1 and 2), and axial error motions are [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], respectively. It is confirmed that the undesirable effects of the form error signals are successfully removed and that the accuracies of the measured spindle error motion components improve.

Measurement Drift in 3-Hole Yaw Pressure Probes From 5µm Sand Fouling at 1050 °C

AbstractThe present paper focuses on the resilience of 3-hole pressure probes to hot sand fouling in turbomachinery environments. These probes are utilized inside jet engine hot sections for diagnostics and flow characterization. Ingestion of sand and other particulates pose a significant risk to hot section components and measurement devices in gas turbine engines. In this study, wedge, cylindrical, and trapezoidal probes were exposed to hot section turbine aerothermal conditions of 1050 °C and 65–70 m/s flow velocity and fouled with 0–5 µm Arizona Road Dust (ARD). Sand accumulated more rapidly on the surface of the trapezoidal and cylindrical probe geometries than on the surface of the wedge probe geometry. Probe calibrations following sand fouling were performed in an ambient temperature, open air, calibration jet at Mach 0.3 and 0.5. Calibration curves using nondimensional coefficients were used to assess probe error in yaw angle due to sand fouling. Probe error was based on each probe’s ability to accurately measure flow direction over a flow angle range of [−10 deg, 10 deg]. On average, the probes displayed greater error at Mach 0.5 than Mach 0.3. The wedge probe performed the best after sand fouling and displayed a maximum error of less than ±2 deg in yaw angle. In contrast, the cylindrical probe performed the worst after sand fouling and displayed maximum errors of more than ±8 deg in yaw angle. Transient response did not change notably with sand fouling.

Moving Array Traffic Probes

This paper explores the potential of moving array 'probes' to collect traffic data. This application simulates the prospect of mining environmental data on traffic conditions to present a cheap and potentially widespread source of traffic conditions. Based on three different simulations, we measure the magnitude and trends of probe error (comparing the probe's `subjective' or time-weighted perception with an `objective' observer) in density, speed, and flow in order to validate the proposed model and compare the results with loop detectors. From these simulations, several conclusions were reached. A single probe's error follows a double hump trend due to an interplay between the factors of traffic heterogeneity and shockwaves. Reduced visibility of the single probe does not proportionately increase the error. Multiple probes do not tend to increase accuracy significantly, which suggests that the data will be still useful even if probes are sparsely distributed. Finally, probes can measure the conditions of oncoming traffic more accurately than concurrent traffic. Further research is expected to consider more complex road networks and develop methods to improve the accuracy of moving array samples.

An adaptive computer-aided path planning to eliminate errors of contact probes on free-form surfaces using a 4-DOF parallel robot CMM and a turn-table

Nowadays, digitizing precise parts consisting of free-form surfaces is essential in geometrical inspections and reverse engineering. Despite the ease of use and high speed of non-contact techniques, contact methods have higher precision. However, using touch probes confront a few difficulties. Various compensation approaches that are often post-processing techniques have been introduced for contact probe errors consisting of ball-tip-radius error, stylus tilt, pre-travel, and probe lobbing. Moreover, in precise applications, achieving satisfying results is difficult and time-consuming.The current paper proposes a computer-aided planning method by implementing a new 4-DOF parallel robot and a cost-effective linear contact probe. This parallel structure exploits three translational DOF and one rotational DOF. Furthermore, the robot is equipped with a precise turn-table. A measuring algorithm for free-form surfaces by normal-to-surface contact has been developed. Evaluating the simulation and the practical measuring results shows excellent feasibly of the method on elimination or great reduction of errors.

Comparison of Three Compensation Methods for the Touch-trigger Probe Pretravel Errors

On-machine inspection (OMI) system has been used extensively for automatic setting of the workpiece and determination of kinematic error in machine tool. There is a necessity not only for knowledge of touch-trigger probing error characteristic, but also for the compensation method of probe error because probing error is an important component of system errors. The comparison of compensation accuracy of three compensation methods is presented. To compensate the touch trigger probe pre-travel errors the calibration experiments with a reference sphere are conducted. Subsequently, the calibration data are used in three compensation methods that the bilinear interpolation method, the bicubic Coons pitch interpolation method and the neural network method. Finally, the validate experiments are conducted on the OMI system, and the compensation results show that the bicubic Coons pitch interpolation method is the most accuracy compensation method.

An accurate probe pre-travel error compensation model for five-axis on-machine inspection system

On a five-axis CNC machine tool, the pretravel errors of touch-trigger probes are severely affected by gravity and must be compensated to ensure the required measurement accuracy. The situation is more complex than that of the three-axis on-machine inspection system. This paper proposes a simple and accurate modeling and compensation method for the probe pretravel error of a five-axis on-machine inspection system. First, the pretravel error for the 5-axis CNC tool is decoupled into three parts, which are analyzed based on the probe's mechanical structure. Then, a new calibration point selection strategy is proposed to obtain the accurate reference sphere center. Finally, we carry out calibration tests to validate the proposed method. The compensation results show that the proposed compensation method for the probe pretravel error under the influence of gravity (PPEUG) can improve the accuracy considerably.

Concurrent atomic force spectroscopy

Force-spectroscopy by atomic force microscopy (AFM) is the technique of choice to measure mechanical properties of molecules, cells, tissues and materials at the nano and micro scales. However, unavoidable calibration errors of AFM probes make it cumbersome to quantify modulation of mechanics. Here, we show that concurrent AFM force measurements enable relative mechanical characterization with an accuracy that is independent of calibration uncertainty, even when averaging data from multiple, independent experiments. Compared to traditional AFM, we estimate that concurrent strategies can measure differences in protein mechanical unfolding forces with a 6-fold improvement in accuracy or a 30-fold increase in throughput. Prompted by our results, we demonstrate widely applicable orthogonal fingerprinting strategies for concurrent single-molecule nanomechanical profiling of proteins.

Triple Probe Error Evaluation Caused by Spatial Separation in the HL-2A Tokamak

The systematic error between the measured electron temperature $T_{e,m}$ and the real electron temperature $T_{e}$ caused by the spatial separation of a triple probe is introduced. The detailed analysis of the systematic error is presented and the relation between $T_{e,m}$ and $T_{e}$ is derived. By comparing the fluctuation of the measured temperature $| \tilde {T}_{e,m}|$ and the real temperature fluctuation $| \tilde {T}_{e}|$ , we find that $| \tilde {T}_{e,m} |\ge | \tilde {T}_{e}|$ . In addition, electron temperature $T_{e}$ , density $n_{e}$ , floating potential $V_{f}$ , and their fluctuation profiles are measured at the edge of HL-2A tokamak with a reciprocating probe system. We experimentally verified that the amplitude of floating potential fluctuation $| \tilde {V}_{f} |$ is about 3 ~ 4 times larger than that of $\boldsymbol {\alpha }| \tilde {T}_{e,m} |$ ; in this condition, we can use the floating potential fluctuation $\tilde {V}_{f}$ to stand for the plasma potential fluctuation $\tilde {V}_{p}$ .

Variable speed compensation method of errors of probes for CNC machine tools

Systematic errors of kinematic touch-trigger probes for CNC machine tools may exceed errors of the machine tool itself. As a result, the machining accuracy is strongly dependent on the probe's accuracy. Numerical correction of probes’ systematic errors can be used. However, it requires executing calculations by the CNC machine tool controller. To avoid this troublesome requirement, a new method of errors compensation is proposed. In this approach, a modification of the probe's pre-travel in a given direction is achieved by modification of measurement speed in this direction. Because all measurement speeds can be calculated offline, the controller does not have to do any calculations. The proposed method has been tested for sample kinematic probes and the error reduction was at least 10-fold.

Investigating the possibilities of compensating systematic errors of three-coordinate touch probes using contact signal

During inspection with three-coordinate touch probes, working on the principle of a kinematic resistance system, the total measuring error called backlash has a negative effect on the measurement accuracy. In order to eliminate the effect of backlash, many companies offer various solutions. As an alternative solution, a new system with improved design of the touch probe and is based on the principle of electrical contacts has been developed. The capabilities and limitations of this new touch probe are analysed in this paper. It is shown that the improved design can reduce the fluctuation of the dislodging force caused by the change of the direction of the force, and the addition of the contact system makes it possible to define the systematic measurement errors.

Bayesian Combined Active/Passive (B-CAP) Soil Moisture Retrieval Algorithm

This paper focused on exploiting remotely sensed active and passive observations over agricultural fields for soil moisture retrieval purposes. Co-polarized backscattering coefficients $\text{HH}$ and $\text{VV}$ and V-polarized brightness temperature $T_{bV}$ measurements were merged onto a Bayesian algorithm to enhance field-based retrieval estimates. The Bayesian algorithm relies on the use of active SAR to constrain passive information. It is assumed that observations are representative of an extent involving field sizes of about 800 m by 800 m, disregarding the scaling issues between the high resolution SAR pixel and the coarse resolution passive pixel. The integral equation model with multiple scattering at second order (IEM2M) and the $\omega \;\text{--}\;\tau$ model were used as forward models for the backscattering coefficients and for the V-polarized brightness temperature, respectively. The Bayesian algorithm was assessed using datasets from the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEx12). Such datasets are representative of contrasting soil conditions since soil moisture spanned almost its whole feasible range from 0.10 to 0.40 cm3 /cm3, at different observation geometries with incidence angles ranging from 35° to 55°. Also, the fairly large amount of measurements (97) made the dataset complete for assessment purposes. Soil moisture variability at field scale and dielectric probe error were accounted for in the comparison between retrieved estimates and in situ measurements. Performance metrics were used to quantify the agreement of the retrieval methodology to in situ information, and to assess the improvement in the combined methodology with respect to the single ones (active or passive). Overall, the root mean squared error (RMSE) showed an improvement from 0.08 to 0.11 cm3/cm3 (only active) or 0.03–0.12 cm3/cm3 (only passive, after bias correction) to 0.06–0.10 cm3/cm3 (combined), thus, demonstrating the potential of such combined soil moisture estimates. When analyzed each field separately, RMSE is less than 0.07 cm 3/cm3 and correlation coefficient $r$ is greater than 0.6 for most of the fields.

Development of NC Machine’s On-Line Inspection Software

Based on Windows operating system, the software of NC machine’s On-line inspection has been developed, the key technology in software development: Set up the comprehensive error model of the inspection system, probe error treatment technology, communication etc. Utilize this software to turn into the procedure of measuring automatically, and can compensate to probe error, the geometric error and thermal error of the machine, have improved the precision and efficiency.

Effects of Thermal Drifts on the Calibration of Capacitive Displacement Probes at the Nanometer Level of Accuracy

The thermal drifts caused by the power dissipated by the mechanical guiding systems are the main limit on the accuracy of an ultrahigh precision cylindricity measuring machine. For this reason, a high-precision compact prototype, henceforth high-precision setup, has been designed to simulate the behavior of the cylindricity measurement machine. It uses in situ calibration of capacitive displacement probes by comparison with four laser interferometers. The setup includes three heating wires for simulating the powers dissipated by the mechanical guiding systems, 19 platinum resistance thermometers (Pt100) to measure temperature propagation inside the setup and four Pt100 sensors to monitor the ambient temperature. The calibration tests carried out under several different conditions reveal that residual errors of the capacitive probes are usually less than 5 nm. The simulation of the cylindricity measurements also indicates that the thermal expansion is a few nanometers.