Roll Errors Research Articles

The Research on the Movement Precision of Globoidal Cam Mechanism Based on Error Modeling

Through analyzing several common errors that have impact on the kinematic accuracy of globoidal cam mechanism, finally a mathematical model of globoidal cam impinged with error was established. By using the differential method, the motion accuracy influence coefficients of the globoid cam mechanism were obtained. The change rule of kinematic accuracy influence coefficient with the change of globoidal cam rotation angle was analysed with practical cases. The analysis result shows: different error factors lead to different influence coefficient; Radius error of the index disc roll has the greatest impact on motion precision, while shaft angle error almost has no influence on the movement precision; The meshing position of the globoidal cam mechanism affects the kinematic accuracy volatile; Moreover, each motion accuracy influence coefficient has a certain relationship with the structure factors of globoidal cam.

Rotational setup errors in pediatric stereotactic radiation therapy

PurposeStereotactic radiation therapy (SRT) is an increasingly commonly used technique in children. The use of image guidance increases the ability to accurately position patients. With our robotic couch, rotational errors that can be corrected are limited to approximately 3 degrees. Given this limitation, we reviewed the rotational setup errors in our pediatric brain tumor population. Methods and MaterialsWe reviewed the rotational corrections for all pediatric (age ≤21 years old) patients treated at our facility from 2009 to 2011. We compared children <5 years old treated to children between 5 and 21 years old (≥5 years old). Also, we analyzed the effect of steroid use and trends in rotational errors over the treatment period in each age group. ResultsThe mean pitch, roll, and yaw rotational setup errors for younger children are −0.70 ± 2.60 degrees, −0.06 ± 1.89 degrees, and 0.69 ± 2.42 degrees, respectively; for children ≥5 years old, they are 0.46 ± 2.09 degrees, −0.06 ± 1.89 degrees, and 0.69 ± 2.42 degrees, respectively. The mean pitch corrections are larger for children <5 years old (P < .001) and the variance of the pitch, roll, and yaw corrections are all larger for children <5 years old (P < .001). The frequency of rotational errors above 3 degrees for pitch, roll, and yaw is 21.7%, 10.6%, and 20.9% for children <5 years old, and 15.6%, 2.1%, and 13.8% for children ≥5 years old. In both age groups, pitch and roll corrections were larger for children treated with steroids. ConclusionsRotational errors in our pediatric population occur more frequently than previously reported, and are more common in younger children and in children treated with steroids. These rotational set up errors may not be fully correctable due to mechanical and safety limitations. We have altered our planning and treatment process to better account for rotational errors in children receiving SRT.

Using High-Resolution Altimetry to Observe Mesoscale Signals

Abstract An Ocean System Simulation Experiment is used to quantify the observing capability of the Surface Water and Ocean Topography (SWOT) mission and its contribution to higher-quality reconstructed sea level anomaly (SLA) fields using optimal interpolation. The paper focuses on the potential of SWOT for mesoscale observation (wavelengths larger than 100 km and time periods larger than 10 days) and its ability to replace or complement altimetry for classical mesoscale applications. For mesoscale variability, the wide swath from SWOT provides an unprecedented sampling capability. SWOT alone would enable the regional surface signal reconstruction as precisely as a four-altimeter constellation would, in regions where temporal sampling is optimum. For some specifics latitudes, where swath sampling is degraded, SWOT capabilities are reduced and show performances equivalent to the historical two-altimeter constellation. In this case, merging SWOT with the two-altimeter constellation stabilizes the global sampling and fully compensates the swath time sampling limitations. Benefits of SWOT measurement are more important within the swath. It would allow a precise local reconstruction of mesoscale structures. Errors of surface signal reconstruction within the swath represent less than 1% (SLA) to 5% (geostrophic velocities reconstruction) of the signal variance in a pessimistic roll error reduction. The errors are slightly reduced by merging swath measurements with the conventional nadir measurements.

Empirical Cross-Calibration of Coherent SWOT Errors Using External References and the Altimetry Constellation

This paper gives an overview of an empirical cross-calibration technique developed for the Surface Water Ocean Topography mission (SWOT). The method is here used to detect and to mitigate two spatially coherent errors in SWOT topography data: the baseline roll error whose signature is linear across track, and the baseline length error whose signature is quadratic across track. Assuming that topography data are corrupted by coherent error signatures that we can model, we extract the signatures, and we empirically use the error estimates to correct SWOT data. The cross-calibration is tackled with a two-step scheme. The first step is to get local estimates over cross-calibration zones, and the second step is to perform a global interpolation of local error estimates and to mitigate the error everywhere. Three methods are used to get local error estimates: 1) we remove a static first guess reference such as a digital elevation model, 2) we exploit overlapping diamonds between SWOT swaths, and 3) we exploit overlapping segments with traditional pulse-limited altimetry sensors. Then, the along-track propagation is performed taking the local estimates as an input, and an optimal interpolator (1-D objective analysis) constrained with a priori statistical knowledge of the problem. The rationale of this paper is to assume that SWOT's scientific requirements are met on all errors but the ones being cross-calibrated. In other words, the algorithms presented in this paper are not needed at this stage of the mission definition, and they are able to deal with higher error levels (e.g., if hardware constraints are relaxed and replaced by additional ground processing). Even in our most pessimistic theoretical scenarios of baseline roll and baseline length errors (up to 70 cm RMS of uncorrected topography error), the cross-calibration algorithm reduces coherent errors to less than 2 cm (outer edges of the swath). Residual errors are subcentimetric for very low-frequency errors (e.g., orbital revolution). Sensitivity tests highlight the benefits of using additional pulse-limited altimeters and optimal inversion schemes when the problem is more difficult to solve (e.g., wavelengths of less than 1000 km), but also to provide a geographically homogeneous correction that cannot be obtained with SWOT's sampling alone.

Development of a grating based multi-degree-of-freedom laser linear encoder using diffracted light

A multi-degree-of-freedom laser linear encoder that can simultaneously measure the position, straightness, pitch, roll, and yaw errors of a linear stage is developed. The proposed laser encoder uses the phase and spatial information of diffracted light. When the light is reflected from a grating and diffracts, the relative movement makes the orders of diffracted light have both phase and spatial geometric variations. The proposed encoder design makes the ±1 order diffracted light interfere and outputs pure sine and cosine wave signals for linear displacement. The ±2 order diffracted light spots are received by two quadrant photodiode detectors and analyzed to inversely calculate the other motion errors. The experimental results show that the measurement error is ±0.6μm for straightness, ±0.8 arcsec for angular error, and ±1.2μm for linear displacement.

Dual Cone-Scanning Horizon Sensor Orbit and Attitude Corrections for Earth Oblateness

I NFRARED-SCANNING horizon sensors are typically used as attitude sensors for spinning and three-axis stabilized satellites. The nadir vector or the nadir angle is determined by detecting the infrared radiation at the horizon with infrared detectors and pencil beams. By integrating the scanning horizon sensors with other sensors, both orbit and attitude can be determined. Examples of such systems include the Microcosm Autonomous Navigation System (MANS) [1,2], which uses dual cone scanners and two slit sun/moon sensors, and the Multimission Attitude Determination and Autonomous Navigation System [3], which employs one scanning horizon sensor and three star sensors. The accuracy of a scanning horizon sensor is limited by random instrumental errors and systematic errors arising from the seasonal variation in Earth’s radiance, the oblate shape of the Earth and satellite altitude variations, the ambient temperature of the sensors, changes in the spin/scan period, and misalignment and biases [4,5]. The random errors can be reduced by increasing the number of measurements that are used in the estimator [6]. However, the systematic errors cannot be reduced in a simple manner. Alex and Shrivastava [4] summarized the error budget for scanning Earth sensors and derived simple relations by using least-squares curve fitting for the on-board correction of systematic errors. With the corrections, the amplitude of the total error is reduced to nearly oneeighth of the original amplitude. Alex and Seshamani [7] established a generalized analytical model of the radiation that can be used to correct the attitude errors induced by the variation of the location and the seasons in Earth’s infrared horizon. Van der Ha [6,8,9], Palimaka et al. [10], Sullivan et al. [11], and Fraiture [12], etc., have studied the effects of bias errors in the sensor measurements and have provided useful methods to reduce the errors. Of these systematic errors, the Earth’s oblateness contributes one of the more significant effects on determination of the nadir vector or the nadir angle [13]. The impact of the oblateness of the Earth on attitude estimation accuracy has been studied in Wertz [14] and the references therein. Roll and pitch errors correction algorithms for the Earth’s oblateness were proposed in Tekawy et al. [13] and Li [15], and also in Hablani [5] with altitude correction, but they all require the satellite’s position information. The impact of the Earth’s oblateness on the nadir vector determination, which can be used for orbit and attitude determination, has not yet been studied. In this note, the systematic error caused by oblateness for a dual cone sensor (DCS) is considered, and the orbit and attitude corrections for the Earth’s oblateness are presented. Compared with themethods described in Hablani [5], Tekawy et al. [13], and Li [15], the problem is transferred from the roll and pitch angle errors’ correction to nadir vector determination around the oblate Earth. According to the principle of measurement, an algorithm determining the nadir vector that accounts for the Earth’s oblateness is derived with the Gauss-Newton method. The nadir vector information, combined with the measurements of other sensors, can be used for orbit determination as well as attitude determination. The nadir vector determination algorithm is verified, and the orbit and attitude corrections for the Earth’s oblateness is illustrated by an integrated algorithm of least-squares orbit determination and twovector attitude determination based on the orientation information of the sun, Earth and moon.

The challenges of designing a lightweight spacecraft structure for landing on the lunar surface

The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has been working with NASA's Marshall Space Flight Center (MSFC) on a lunar lander design that would take scientific measurements on the surface of the moon. This effort is part of NASA's Robotic Lunar Lander (RLL) Development Project. The requirements imposed on the design of the lander are: (1) Provide a lightweight lander structure to minimize the launch costs and maximize the payload carrying capability, (2) Minimize the lander launch envelope to allow for launching multiple landers on a single launch vehicle, (3) Given specific approach velocities, design a lander with geometric properties (low center-of-gravity, etc.) that maximizes the chances for a controlled landing on the lunar surface, (4) Provide a stable platform for all of the various scientific instruments. The lightweight lander requirement originates from the desire to minimize the launch costs and possibly package multiple landers on a single launch vehicle. The use of lightweight composite materials and advanced manufacturing techniques are employed throughout the design and construction of the structure in order to minimize mass and maximize structural stiffness. Minimizing the launch envelope enables the potential packaging of several spacecraft into one launch vehicle shroud. By having multiple landers, the scientific return is enhanced. Multiple spacecraft on the lunar surface provides independent confirmation of science measurements taken and also highlights any variance in the science data taken at differing lunar latitudes. Naturally, the launch cost per lander is greatly reduced if more than one lander can be packaged on a single launch vehicle. The lunar lander vehicle must arrive at the lunar surface at an upright orientation. In order to accomplish this, the structure geometry must be designed to accommodate attitude errors in roll, pitch and yaw. In addition, the structure must be able to withstand various landing scenarios, which include a wide range of landing velocities, decelerations and attitude rates. The stability requirement is dictated by the nature of the instrument suite. Many of the measurements to be taken on the lunar surface are so sensitive that any mechanical disturbances could potentially corrupt the measured data. Mechanical disturbances such as operating mechanisms, thermal expansion/contraction, deployable booms or other devices must be minimized. It is imperative that all of the structural requirements are met for this mission. Failure to meet any of the numerous challenging requirements could cause the loss of all the scientific objectives.

A Novel Method for Roll Error Measurement of a Linear Worktable of a Machine Tool

This paper proposes a multi-step and multi-probe method to measure the roll error of a linear worktable during its movement. Two displacement sensors are used and two measurement steps are employed. Compared with two displacement sensors and a sensing target with high flatness method or a method using autocollimator, this method is in low cost and easier to be carried out. In proposed system, the slope information of roll error is obtained by sensor fusion technology. Roll error estimation algorithm is derived, and sequential-two-point method is used to sample sensors’ signal. Simulation and experimental results show the feasibility of the proposed method.

Determination of Load-Sharing Displacement of Flexible Pin Roll in Planet Gear Train

The eccentricity errors of each piece in the planet gear train set are described. This paper has made a tentative study on the determination of load-sharing displacement with formulas of equivalent errors. It takes the flexible pin roll as the load-sharing piece and LevelⅡ planet gear drive in the speed-increasing gearbox of some wind power generator for the case study. The results show i) that the radial error of each piece does not influence the operation of the planet gear train, but the tangential error does influence the load-sharing among the planet gears; and ii) that the load sharing displacement is determined by the centering tangential equivalent error of the flexible pin roll, which may provide reference to projects.

Linear diffraction grating interferometer with high alignment tolerance and high accuracy

We present an innovative structure of a linear diffraction grating interferometer as a long stroke and nanometer resolution displacement sensor for any linear stage. The principle of this diffractive interferometer is based on the phase information encoded by the ±1st order beams diffracted by a holographic grating. Properly interfering these two beams leads to modulation similar to a Doppler frequency shift that can be translated to displacement measurements via phase decoding. A self-compensation structure is developed to improve the alignment tolerance. LightTool analysis shows that this new structure is completely immune to alignment errors of offset, standoff, yaw, and roll. The tolerance of the pitch is also acceptable for most installation conditions. In order to compact the structure and improve the signal quality, a new optical bonding technology by mechanical fixture is presented so that the miniature optics can be permanently bonded together without an air gap in between. For the output waveform signals, a software module is developed for fast real-time pulse counting and phase subdivision. A laser interferometer HP5529A is employed to test the repeatability of the whole system. Experimental data show that within 15 mm travel length, the repeatability is within 15 nm.

An Optimized System for Interventional Magnetic Resonance Imaging-Guided Stereotactic Surgery

Deep brain stimulation electrode placement with interventional magnetic resonance imaging (MRI) has previously been reported using a commercially available skull-mounted aiming device (Medtronic Nexframe MR) and native MRI scanner software. This first-generation method has technical limitations that are inherent to the hardware and software used. A novel system (SurgiVision ClearPoint) consisting of an aiming device (SMARTFrame) and software has been developed specifically for interventional MRI, including deep brain stimulation. To report a series of phantom and cadaver tests performed to determine the capability, preliminary accuracy, and workflow of the system. Eighteen experiments using a water phantom were used to determine the predictive accuracy of the software. Sixteen experiments using a gelatin-filled skull phantom were used to determine targeting accuracy of the aiming device. Six procedures in 3 cadaver heads were performed to compare the workflow and accuracy of ClearPoint with Nexframe MR. Software prediction experiments showed an average error of 0.9 ± 0.5 mm in magnitude in pitch and roll (mean pitch error, -0.2 ± 0.7 mm; mean roll error, 0.2 ± 0.7 mm) and an average error of 0.7 ± 0.3 mm in X-Y translation with a slight anterior (0.5 ± 0.3 mm) and lateral (0.4 ± 0.3 mm) bias. Targeting accuracy experiments showed an average radial error of 0.5 ± 0.3 mm. Cadaver experiments showed a radial error of 0.2 ± 0.1 mm with the ClearPoint system (average procedure time, 88 ± 14 minutes) vs 0.6 ± 0.2 mm with the Nexframe MR (average procedure time, 92 ± 12 minutes). This novel system provides the submillimetric accuracy required for stereotactic interventions, including deep brain stimulation placement. It also overcomes technical limitations inherent in the first-generation interventional MRI system.

A New Method to Correct Pushbroom Hyperspectral Data Using Linear Features and Ground Control Points

Data acquired using aerial pushbroom scanners often contain aircraft motion errors—especially aircraft roll error. This article describes a new algorithm to correct roll errors using both ground control points and linear features digitized on a reference map and the uncorrected image. The algorithm is different from previous methods used to correct aerial pushbroom data because it does not solely rely on a single or multiple straight lines. Rather, it is able to integrate both points and lines together to correct the error. With an associated loss of precision, it can also use points or lines separately. The method is tested on a hyperspectral dataset acquired in the Range Creek, Utah area during June 2009. It was found that the approach is an effective way to remove aircraft roll errors and prepare the image for additional georegistration. A program with a graphical user interface has been written using the algorithm and is available on the project's website.

Roll Orientation Estimator for Smart Projectiles Using Thermopile Sensors

The use of inexpensive, commercially available thermopiles sensors for roll orientation estimation of spinning bodies is explored. The sensors convert observed thermal gradients into an electrical signal well suited for onboard data acquisition and real-time signal processing. An environmental model emulating sensor stimulus for a six-degree-of-freedom body is generated given standard atmospheric and typical ground conditions. When sensor characteristics are included, the fully developed model can be used to generate accurate sensor output as a function of Euler angles and altitude. Outputs from the model are then shown to compare favorably with experimental flight data, capturing the predominant and nearly sinusoidal signal variation as the projectile rolls. An extended Kalman filter algorithm is offered, which enables real-time roll angle and roll rate estimation using solely thermopiles as feedback. Example results demonstrate that the algorithm yields reasonably accurate roll information. Finally, a trade study demonstrates that roll error is further mitigated as the number of thermopile sensors is increased. This research shows that thermopiles could be useful in a diverse multisensor constellation as a convenient absolute inertial roll reference.

Simulation of beam size multiknobs correction at the Accelerator Test Facility 2 at KEK

The ATF2 project is the final focus system prototype for the ILC and CLIC linear collider projects, with a purpose of reaching a 37 nm vertical beam size at the interaction point (IP). During the initial commissioning, we started with larger-than-nominal β-functions at the IP in order to reduce the effects from higher-order optical aberrations and thereby simplifying the optical corrections needed. We report on the simulation studies at two different IP locations developed based on waist scan, dispersion, coupling and β function multiknobs correction in the large β optics of ATF2, in the presence of two kinds of magnet inaccuracies (quadrupole gradient and roll errors) to generate all possible linear optic distortions at the IP. A vertical beam size which is very close to the nominal beam size is obtained based on the simulation study.

Fixed‐wing attitude estimation using temporal tracking of the horizon and optical flow

AbstractA method has been developed for estimating pitch angle, roll angle, and aircraft body rates based on horizon detection and temporal tracking using a forward‐looking camera, without assistance from other sensors. Using an image processing front end, we select several lines in an image that may or may not correspond to the true horizon. The optical flow at each candidate line is calculated, which may be used to measure the body rates of the aircraft. Using an extended Kalman filter (EKF), the aircraft state is propagated using a motion model and a candidate horizon line is associated using a statistical test based on the optical flow measurements and the location of the horizon. Once associated, the selected horizon line, along with the associated optical flow, is used as a measurement to the EKF. To test the accuracy of the algorithm, two flights were conducted, one using a highly dynamic uninhabited airborne vehicle (UAV) in clear flight conditions and the other in a human‐piloted Cessna 172 in conditions in which the horizon was partially obscured by terrain, haze, and smoke. The UAV flight resulted in pitch and roll error standard deviations of 0.42 and 0.71 deg, respectively, when compared with a truth attitude source. The Cessna flight resulted in pitch and roll error standard deviations of 1.79 and 1.75 deg, respectively. The benefits of selecting and tracking the horizon using a motion model and optical flow rather than naively relying on the image processing front end are demonstrated. © 2011 Wiley Periodicals, Inc.

A three-axis autocollimator for detection of angular error motions of a precision stage

This paper presents a new autocollimator that can simultaneously detect the three-axis angular error motions (pitch, yaw, and roll errors) of a precision linear stage. A collimated laser beam from a laser diode is projected onto a grating reflector mounted on the stage. The reflected 0th-order diffracted beam is received by an autocollimation unit, which consists of a collimator objective and a quadrant photodiode, for detecting the pitch and yaw errors. The reflected 1st-order diffracted beam is received by another autocollimation unit for detecting the roll error. Experiments were carried out to evaluate the basic performance of the prototype sensor.

Evaluation of rotational set-up errors in patients with thoracic neoplasms

Objective To assess the rotational set-up errors in patients with thoracic neoplasms. Methods 224 kilovohage cone-beam computed tomography (KVCBCT) scans from 20 thoracic tumor pa-tients were evaluated retrospectively. All these patients were involved in the research of Evaluation of the residual set-up error for online kilovohage cone-beam CT guided thoracic tumor radiation. Rotational set-up errors, including pitch, roll and yaw, were calculated by 'aligning the KVCBCT with the planning CT, using the semi-automatic alignment method. Results The average rotational set-up errors were -0.28°±1.52°, 0.21°± 0.91° and 0.27°± 0. 78° in the left-fight, superior-inferior and anterior-posterior axis, respective-ly. The maximal rotational errors of pitch, roll and yaw were 3.5°, 2.7° and 2.2°, respectively. After cor-rection for translational set-up errors, no statistically significant changes in rotational error were observed. Conclusions The rotational set-up errors in patients with thoracic neoplasms were all small in magnitude. Rotational errors may not change after the correction for translational set-up errors alone, which should be e-valuated in a larger sample future. Key words: Thoracic neoplasms/radiotherapy; Rotational set-up error; Tomography,X-ray computed,kilovohage cone-beam

Development of a middle-range six-degrees-of-freedom system

This paper describes the successful development of a middle-range six-degrees-of-freedom stage, using the features of a flexible structure. The system includes two parts: a middle-range positioning X— Y stage and a four-degrees-of-freedom stage. The flexible structure of the four-degrees-of-freedom stage is built from two kinds of flexible bodies: circular hinges and a new two-degrees-of-freedom flexible body. The four-degrees-of-freedom stage was designed to compensate movement errors including linear displacement, pitch, and roll errors. The linear displacement reaches 20 mm along the X-axis, 20 mm along the Y-axis, and 5 μm along the Z-axis. The rotation angle around the X-axis (θ x), Y-axis (θ y), and Z-axis (θ z) were all 10 arcsec. A novel six-degrees-of-freedom measuring system was also designed. Precision feedback control is demonstrated in a series of experiments performed using the proposed measurement system.

템플릿 정합과 B-Spline 보간에 의한 3차원 광학 영상 처리

본 논문에서는 비젼을 이용한 영상처리 기술을 기반으로 비접촉식 미세 측정 광학기에 의해 측정된 이미지를 템플릿 매칭과 B-Spline 보간법에 의해 보다 빠르고, 정밀한 복원 기법을 제안한다. 이를 위해 먼저 각각의 이미지로부터 매칭 템플릿과 피 매칭 템플릿을 검출한다. 그런 다음 기준면으로부터 두 이미지의 중첩되는 부분의 롤, 피치, 요 오차를 보정하여 정합시킨다. 그리고 B-Spline 보간법에 의해 정합된 부분을 연속화한다. 마지막으로, 제안된 방법은 실험을 통해 그 응용 가능성을 증명한다. The purposes of this paper is to propose new techniques to reconstruct measured optical images by using the template matching and B-Spline interpolation method based on image processing technology. To do this, we detect the matching template and non-matching template from each optical image. And then, we match the overlaped images from base level by correcting roll, pitch, and yaw error of images. At last, the matching image is interpolated by B-Spline interpolation. Finally, we show the effectiveness and feasibility of the proposed method through some experiments.

Nonlinear Constraint Network Optimization for Efficient Map Learning

Learning models of the environment is one of the fundamental tasks of mobile robots since maps are needed for a wide range of robotic applications, such as navigation and transportation tasks, service robotic applications, and several others. In the past, numerous efficient approaches to map learning have been proposed. Most of them, however, assume that the robot lives on a plane. In this paper, we present a highly efficient maximum-likelihood approach that is able to solve 3-D and 2-D problems. Our approach addresses the so-called graph-based formulation of simultaneous localization and mapping (SLAM) and can be seen as an extension of Olson's algorithm toward non-flat environments. It applies a novel parameterization of the nodes of the graph that significantly improves the performance of the algorithm and can cope with arbitrary network topologies. The latter allows us to bound the complexity of the algorithm to the size of the mapped area and not to the length of the trajectory. Furthermore, our approach is able to appropriately distribute the roll, pitch, and yaw error over a sequence of poses in 3-D mapping problems. We implemented our technique and compared it with multiple other graph-based SLAM solutions. As we demonstrate in simulated and real-world experiments, our method converges faster than the other approaches and yields accurate maps of the environment.