Absolute Positional Accuracy Research Articles

Development of a new neurosurgical 5-DOF parallel robot for stereotactic DBS operations

In this study, a new 5-degree of freedom parallel-type robot for neurosurgery is developed and investigated for potential application in deep brain surgery (DBS). The neurosurgical robot consists of the base plate, the moving plate, and three limbs (a PPPU type central limb and two SPS type side limbs) connecting the plates. With an intension to use the developed neurosurgical micro robot with a macro scale robot, the position and kinematic analyses of the macro–micro robot are conducted. A structural analysis under the maximum payload condition is also conducted to confirm its structural rigidity. Then, a macro–micro robot simulator that employs the prototype as a micro robot module is developed to test both its motion capability and its potential application as a stereotactic DBS device. Finally, the absolute position accuracy measurement of the developed micro robot module based on its identified kinematic calibration model verified that its accuracy is comparable to those of existing micro robot module candidates.

Error Analysis and Experimental Study of a Bi-Planar Parallel Mechanism in a Pedicle Screw Robot System.

Due to the urgent need for high precision surgical equipment for minimally invasive spinal surgery, a novel robot-assistant system was developed for the accurate placement of pedicle screws in lumbar spinal surgeries. The structure of the robot was based on a macro-micro mechanism, which includes a serial mechanism (macro part) and a bi-planar 5R parallel mechanism (micro part). The macro part was used to achieve a large workspace, while the micro part was used to obtain high stiffness and accuracy. Based on the transfer function of dimension errors, the factors affecting the accuracy of the end effectors were analyzed. Then the manufacturing errors and joint angle error on the position-stance of the end effectors were investigated. Eventually, the mechanism of the strain energy produced by the deformation of linkage via forced assembly and displacements of the output point were calculated. The amount of the transfer errors was quantitatively analyzed by the simulation. Experimental tests show that the error of the bi-planar 5R mechanism can be controlled no more than 1 mm for translation and 1° for rotation, which satisfies the required absolute position accuracy of the robot.

Positional error similarity analysis for error compensation of industrial robots

The purpose of this paper is to propose an error compensation method with error similarity analysis to improve the absolute positional accuracy of industrial robots. The positional error similarity is proposed with the analysis of the error model established by robot kinematic parameters, and is quantified with semivariogram function. Then an error compensation method is proposed base-on positional error similarity. The ordinary Kriging method is used to calculate the positional errors of the robot TCP. The error compensation is performed by modifying the position coordinates in the robot controlling commands. Experimental verification showed that the maximum positional error of the robot TCP was reduced by 75.36% from 1.2912mm to 0.3182mm.

An error-similarity-based robot positional accuracy improvement method for a robotic drilling and riveting system

It is important to improve the absolute positional accuracy of the industrial robots used in the robotic drilling and riveting systems. The purpose of this paper is to propose a method to compensate for the absolute positional errors of the industrial robots. Firstly, the spatial similarity of the positional errors is qualitatively and quantitatively analyzed using semivariogram function and experiments. Secondly, the positional error model is established based on the spatial similarity, and a linear unbiased optimal estimation method of the target positional errors is proposed. Finally, experiments are used to verify the proposed methods with measuring the robot’s positional errors after compensation. The analysis shows that there is a spatial similarity of positional errors in the robot joint space, which can be used to establish error model and to estimate the target’s positional errors. Experimental results show that the proposed method can reduce the maximum absolute positional errors by 84.08 % from 2.01 to 0.32 mm, which can meet the accuracy requirements of the robotic drilling and riveting system.

High-precision positioning of radar scatterers

Remote sensing radar satellites cover wide areas and provide spatially dense measurements, with millions of scatterers. Knowledge of the precise position of each radar scatterer is essential to identify the corresponding object and interpret the estimated deformation. The absolute position accuracy of synthetic aperture radar (SAR) scatterers in a 2D radar coordinate system, after compensating for atmosphere and tidal effects, is in the order of centimeters for TerraSAR-X (TSX) spotlight images. However, the absolute positioning in 3D and its quality description are not well known. Here, we exploit time-series interferometric SAR to enhance the positioning capability in three dimensions. The 3D positioning precision is parameterized by a variance–covariance matrix and visualized as an error ellipsoid centered at the estimated position. The intersection of the error ellipsoid with objects in the field is exploited to link radar scatterers to real-world objects. We demonstrate the estimation of scatterer position and its quality using 20 months of TSX stripmap acquisitions over Delft, the Netherlands. Using trihedral corner reflectors (CR) for validation, the accuracy of absolute positioning in 2D is about 7 cm. In 3D, an absolute accuracy of up to ?66 cm is realized, with a cigar-shaped error ellipsoid having centimeter precision in azimuth and range dimensions, and elongated in cross-range dimension with a precision in the order of meters (the ratio of the ellipsoid axis lengths is 1/3/213, respectively). The CR absolute 3D position, along with the associated error ellipsoid, is found to be accurate and agree with the ground truth position at a 99% confidence level. For other non-CR coherent scatterers, the error ellipsoid concept is validated using 3D building models. In both cases, the error ellipsoid not only serves as a quality descriptor, but can also help to associate radar scatterers to real-world objects.

Seismic velocity structure and earthquake relocation for the magmatic system beneath Long Valley Caldera, eastern California

A new three-dimensional (3-D) seismic velocity model and high-precision location catalog for earthquakes between 1984 and 2014 are presented for Long Valley Caldera and its adjacent fault zones in eastern California. The simul2000 tomography algorithm is applied to derive the 3-D Vp and Vp/Vs models using first-arrivals of 1004 composite earthquakes obtained from the original seismic data at the Northern California Earthquake Data Center. The resulting Vp model reflects geological structures and agrees with previous local tomographic studies. The simultaneously resolved Vp/Vs model is a major contribution of this study providing an important complement to the Vp model for the interpretation of structural heterogeneities and physical properties in the study area. The caldera is dominated by low Vp anomalies at shallow depths due to postcaldera fill. High Vp and low Vp/Vs values are resolved from the surface to ~3.4km depth beneath the center of the caldera, corresponding to the structural uplift of the Resurgent Dome. An aseismic body with low Vp and high Vp/Vs anomalies at 4.2–6.2km depth below the surface is consistent with the location of partial melt suggested by previous studies based on Vp models only and the inflation source locations based on geodetic modeling. The Sierran crystalline rocks outside the caldera are generally characterized with high Vp and low Vp/Vs values. The newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high-precision earthquake catalog based on similar-event cluster analysis and waveform cross-correlation data. The fine-scale velocity structure and precise earthquake relocations are useful for investigating magma sources, seismicity and stress interaction and other seismological studies in Long Valley.

Alternative Solutions for RTK-GPS Applications in Building and Road Constructions

Currently, Global Positioning System (GPS) techniques are becoming a much larger part of the surveying industry. Many companies are now using GPS in their everyday work activities. The Real Time Kinematic (RTK) positioning is an integral part of topographic surveys, road surveying, constructions and most civil engineering applications. Normally, RTK can be used to collect the positioning data successfully and quickly. The civil and construction projects are designed in ground distances while RTK measurements are done in grid coordinate system, in which the distances between points are different from ground. The RTK measurements should be converted to ground for compatibility with the designed. In this paper, the accuracy of three alternatives for converting RTK measurements to ground was studied. These alternatives are, using scale factor, using two ground reference points and using Low Distortion Projection (LDP) surface. For the accuracy investigation purpose, a traverse of 14 points elongated for a distance of about 1400 m was constructed. Its coordinates were measured using total station, then the misclosure error was computed and the coordinates were adjusted. The traverse points coordinates were measured again using RTK_GPS considering one of them as base point. The three studied alternatives were applied and the results were compared. The results show that the accuracy of the three alternatives is ranging from 2.1 to 2.9 cm in the relative position of points to the base point. For absolute position accuracy, the two ground reference points alternative is the most accurate alternative with an average error of 3.8 cm while the other two alternatives are almost the same with an average error of 12.3 cm.

Automatic Modification of Local Drilling Holes via Double Pre-Assembly Holes

Manufacturing accuracy, especially position accuracy of fastener holes, directly affects service life and security of aircraft. The traditional modification has poor robustness, while the modification based on laser tracker costs too much. To improve the relative position accuracy of aircraft assembly drilling, and ensure the hole-edge distance requirement, a method was presented to modify the coordinates of drilling holes. Based on online inspecting two positions of pre-assembly holes and their theoretical coordinates, the spatial coordinate transformation matrix of modification could be calculated. Thus the straight drilling holes could be modified. The method improves relative position accuracy of drilling on simple structure effectively. And it reduces the requirement of absolute position accuracy and the cost of position modification. And the process technician also can use this method to decide the position accuracy of different pre-assembly holes based on the accuracy requirement of assembly holes.

A new atmospheric GNSS method for improving the absolute positioning accuracy

A new method for positioning a signal receiver of the global navigation satellite system is proposed within the ray theory and under the assumption that the atmosphere is spherically stratified and the dependence of the speed of the radio signal sent by each navigation satellite on the distance from the center of the Earth is known. A new basic system of equations is presented. For the minimum number of four navigation satellites, it consists of eight equations in eight unknowns, four of which are accessory ray parameters. The correctness of the new basic system is proved, and an algorithm for its solution is described. The purpose of the new method is a significant improvement in the accuracy of the absolute positioning of the signal receiver of the global navigation satellite system through the proper account of irregularities of the ionosphere and troposphere.

Practical Earthquake Location on a Continental Scale in Australia Using the AuSREM 3D Velocity Model

This study explores the full 3D earthquake location for the Australian continent, exploiting the recent 3D Australian Seismological Reference Model (AuSREM). Seismic velocities from AuSREM were used as input to precompute finely spaced P ‐ and S ‐travel‐time grids for each station in the Australian National Seismograph Network using the multistage fast marching method. Travel times from anywhere in the grid to the corresponding station can then be computed by interpolation. The location search using these travel times is based on matching observed and computed arrival times using the neighborhood algorithm. All computations involved can be performed in practical time frames on a single processor computer. The performance of the 3D approach relative to location using the 1D global ak135 velocity model was assessed by locating a set of recent earthquakes. The arrival‐time residuals for P and S arrivals are significantly smaller when using the 3D AuSREM model. The improvements over ak135 are especially large in the 10°–18° distance range, in which a distance bias is strongly reduced and for those paths where the ak135 residuals are large. A small set of six ground‐truth events was used to assess to what extent the reduction in travel‐time residuals leads to better absolute location accuracy. The 3D location offset from the ground‐truth position is typically half that of the ak135 offset. The patterns of offsets suggest that the already fast mantle wavespeeds in western Australia need to be even faster than in AuSREM.

A distance error based industrial robot kinematic calibration method

Purpose– The purpose of this paper is to present a distance accuracy-based industrial robot kinematic calibration model. Nowadays, the repeatability of the industrial robot is high, while the absolute positioning accuracy and distance accuracy are low. Many factors affect the absolute positioning accuracy and distance accuracy, and the calibration method of the industrial robot is an important factor. When the traditional calibration methods are applied on the industrial robot, the accumulative error will be involved according to the transformation between the measurement coordinate and the robot base coordinate.Design/methodology/approach– In this manuscript, a distance accuracy-based industrial robot kinematic calibration model is proposed. First, a simplified kinematic model of the robot by using the modified Denavit–Hartenberg (MDH) method is introduced, then the proposed distance error-based calibration model is presented; the experiment is set up in the next section.Findings– The experimental results show that the proposed calibration model based on MDH and distance error can improve the distance accuracy and absolute position accuracy dramatically.Originality/value– The proposed calibration model based on MDH and distance error can improve the distance accuracy and absolute position accuracy dramatically.

FT-IR spectra of 17O-enriched CO2 in the ν3 region: High accuracy frequency calibration and spectroscopic constants for 16O12C17O, 17O12C17O, and 17O12C18O

We report new Fourier transform infrared (FT-IR) spectroscopy measurements of the 17O-enriched isotopologues of CO2 in the ν3 region (2200–2450cm−1, 65–75THz) with absolute calibration accuracies better than 3×10−6cm−1 (∼100kHz) for strong, isolated transitions. Spectra were obtained using the JPL Bruker IFS-125HR Fourier Transform Spectrometer (JPL-FTS). The JPL-FTS performance was achieved by vigorously maintaining the optical alignment, regularly monitoring its modulation efficiency while minimizing phase errors to deliver absolute frequency calibration and line position accuracies comparable to typical sub-millimeter/THz spectroscopy. Fits of the 00011←00001 fundamental bands for 16O12C17O (627), 17O12C17O (727), and 17O12C18O (728) were obtained with RMS residual values of 2.9×10−6cm−1 for all three isotopologues. These results provide a complete and accurate set of transition frequencies required for remote sensing of planetary atmospheres, especially Venus and Mars, and represent a new level of Doppler measurement accuracies.

Absolute robot calibration with a single telescoping ballbar

• A new method and device for measuring a set of poses was recently proposed. • The device consists of a telescoping ballbar and 2 fixtures, each with 3 magnetic cups. • This paper presents the absolute calibration of an industrial robot with this device. • The performance of the method is measured in 9.905 robot poses with a laser tracker. • The method proposed is compared to the standard one based on the use of a laser tracker. A novel 6D measurement system was recently proposed, comprising a single commercially available telescoping ballbar and two custom-made fixtures. One fixture is attached to the robot base and the other to the robot end-effector, and each having three magnetic cups. In each of 72 poses of the tool fixture, with respect to the base fixture, it is possible to measure six distances with the ballbar between the magnetic cups on the tool fixture and the magnetic cups on the base fixture, and thus calculate the pose with high accuracy. This paper is the first to present the successful use of this measurement system for absolute robot calibration. The robot calibrated is a Fanuc LR Mate 200iC six-axis industrial robot and the telescoping bar used is the QC20-W by Renishaw . The absolute position accuracy of the robot after calibration is validated with a Faro laser tracker in almost 10,000 robot configurations. Considering the validation data in only the front/up configurations, the mean absolute positioning error is improved from 0.873 mm to 0.479 mm. To allow a comparison, the robot is also calibrated using the laser tracker and the robot accuracy validated in the same 10,000 robot configurations.

Instrument study of the Lunar Dust eXplorer (LDX) for a lunar lander mission

One of the highest-priority issues for a future human or robotic lunar exploration is the lunar dust. This problem should be studied in depth in order to develop an environment model for a future lunar exploration. A future ESA lunar lander mission requires the measurement of dust transport phenomena above the lunar surface. Here, we describe an instrument design concept to measure slow and fast moving charged lunar dust which is based on the principle of charge induction. LDX has a low mass and measures the speed and trajectory of individual dust particles with sizes below one micrometer. Furthermore, LDX has an impact ionization target to monitor the interplanetary dust background. The sensor consists of three planes of segmented grid electrodes and each electrode is connected to an individual charge sensitive amplifier. Numerical signals were computed using the Coulomb software package. The LDX sensitive area is approximately 400cm2. Our simulations reveal trajectory uncertainties of better than 2° with an absolute position accuracy of better than 2mm.

Joint Stiffness Identification and Flexibility Compensation of Articulated Industrial Robot

Articulated robots are the most common industrial robots for their large workspace and flexibility. However, the existence of joint flexibility makes those robots difficult to achieve high absolute position accuracy. This paper presents a method to identify the joint stiffness of the robot. The basic idea of that method is to get joint stiffness based on Hooks Law through stepping movement of a single joint and calculating the corresponding joint gravity torque of every step. The practicality of that method is verified by experiment and a plan is carried out to compensate the joint flexibility.

Assessing The Positional Accuracy Of Airborne Laser Scanning in urban areas

AbstractA new method for assessment of the absolute positional accuracy of lidar point clouds is described. It is based on the plane surfaces of building roofs which are derived from laser footprints. Three such planes intersect at a point and the coordinates of several of these well‐defined points are compared with points determined from aerial photography. From the differences obtained accuracy measures are derived. An analysis regarding the type of error distribution is carried out in order to determine whether to apply either standard or robust accuracy measures. Confidence intervals are derived for each accuracy measure by means of a unique computational method. A practical test with the proposed method revealed a high precision in the intersected points. The absolute positional accuracy of the lidar point cloud was determined with both standard and robust accuracy measures; the latter always produced smaller values. Suggestions for standards in the assessment of the positional accuracy of laser point clouds are made.

A simple, interactive GIS tool for transforming assumed total station surveys to real world coordinates – the CHaMP transformation tool

Increasingly, geoscientists and biologists are monitoring the natural environment with total station and terrestrial laser scanning surveys. Due to the remote nature of many of the sites monitored (e.g., streams, rivers, glaciers, etc.) the surveys are often done in unprojected, Cartesian, local, assumed coordinate systems. However, without the survey data projected in real world coordinates the range of possible analyses is limited and the contextual power of existing imagery, elevation models, and hydrologic layers can not be exploited. This requires a transformation from the local assumed to the real world coordinate systems. We present a simple interactive interface, as an ArcGIS Add-In, that allows a user to transform unprojected total station data into real-world coordinates using three benchmark coordinates, which can be collected from a hand-held GPS (available at http://ctt.joewheaton.org/). Unlike most transformations built into GIS programs, our tool uses an affine transformation (simple shift and rotate) to preserve the precision and relative accuracy of the total station survey, while leveraging the absolute positional accuracy of the hand-held GPS to place one's data approximately in real world coordinates for GIS overlay purposes. The user can quickly visually inspect between six and twelve transformation options, while comparing the residual error estimates to interactively choose the most reasonable transformation. The tool provides an easy-to-use, cost-effective workflow, which facilitates the sharing and visualization of precise total station survey data in real world coordinates through a webGIS or virtual globes (e.g., Google Earth, NASA Whirlwind). The tool has been tested and was used by 12 crews to transform topographic total station surveys of 364 sites into real world coordinates as part of the Columbian Habitat Monitoring Program (CHaMP).

Absolute Orbit and Gravity Determination Using Relative Position Measurements Between Two Satellites

A method has been developed to use a time series of relative position measurements to estimate the orbits of two satellites along with corrections to the gravity model of the celestial body about which they orbit. This system provides autonomy or near autonomy and could be used for gravity recovery at the Moon or a planet. This system eliminates the need for a third spacecraft that maintains a constant link with Earth-based tracking stations when the two probe spacecraft pass to the far side of the body whose gravity model is being estimated. The system uses a radio cross link to measure the relative range between the two satellites. It uses an optical imaging device on one of the satellites, such as a star camera, and a light beacon on the other satellite in order to measure the relative bearing between the satellites referenced to inertial coordinates. The two satellites’ orbits and corrections to the gravity field model are shown to be absolutely observable in cases where the two orbital altitude time histories are not identical. An extended Kalman filter for this system is developed, and it is tested using data from a truth-model simulation. The resulting system can achieve absolute RMS position accuracies of 3.5 m, absolute RMS velocity accuracies of 0.003 m/s, and RMS gravity accuracies of 3x10 -7 m/s 2 when operating on a month’s worth of data from a pair of Lunar orbiting spacecraft.

Calibration Methods of Planar Parallel Robot

Kinematic calibration is an effective method of improving robotic absolute position accuracy by means of measurement, identification and compensation etc. This paper investigates the technology of kinematic calibration and error compensation for the 2-DOF planar parallel robot. A multi-step calibration method is presented based on error itterative method and nonlinear optimum method. Experimental results indicate that the proposed method can effectively compensate position error of the robot in Oxy plane, and the absolute position error of the calibrated robot is less than 6μm.

Reconstruction of brachytherapy seed positions and orientations from cone-beam CT x-ray projections via a novel iterative forward projection matching method

To generalize and experimentally validate a novel algorithm for reconstructing the 3D pose (position and orientation) of implanted brachytherapy seeds from a set of a few measured 2D cone-beam CT (CBCT) x-ray projections. The iterative forward projection matching (IFPM) algorithm was generalized to reconstruct the 3D pose, as well as the centroid, of brachytherapy seeds from three to ten measured 2D projections. The gIFPM algorithm finds the set of seed poses that minimizes the sum-of-squared-difference of the pixel-by-pixel intensities between computed and measured autosegmented radiographic projections of the implant. Numerical simulations of clinically realistic brachytherapy seed configurations were performed to demonstrate the proof of principle. An in-house machined brachytherapy phantom, which supports precise specification of seed position and orientation at known values for simulated implant geometries, was used to experimentally validate this algorithm. The phantom was scanned on an ACUITY CBCT digital simulator over a full 660 sinogram projections. Three to ten x-ray images were selected from the full set of CBCT sinogram projections and postprocessed to create binary seed-only images. In the numerical simulations, seed reconstruction position and orientation errors were approximately 0.6 mm and 5 degrees, respectively. The physical phantom measurements demonstrated an absolute positional accuracy of (0.78 +/- 0.57) mm or less. The theta and phi angle errors were found to be (5.7 +/- 4.9) degrees and (6.0 +/- 4.1) degrees, respectively, or less when using three projections; with six projections, results were slightly better. The mean registration error was better than 1 mm/6 degrees compared to the measured seed projections. Each test trial converged in 10-20 iterations with computation time of 12-18 min/iteration on a 1 GHz processor. This work describes a novel, accurate, and completely automatic method for reconstructing seed orientations, as well as centroids, from a small number of radiographic projections, in support of intraoperative planning and adaptive replanning. Unlike standard back-projection methods, gIFPM avoids the need to match corresponding seed images on the projections. This algorithm also successfully reconstructs overlapping clustered and highly migrated seeds in the implant. The accuracy of better than 1 mm and 6 degrees demonstrates that gIFPM has the potential to support 2D Task Group 43 calculations in clinical practice.