Rotation Angle Error Research Articles

Measurement and analysis of typical motion error traces from a circular test

The circular test provides a rapid and efficient way of measuring the contouring accuracy of a machine tool. To get the actual point coordinate in the work plane, an improved measurement instrument - a new ball bar test system - is presented in this paper to identify both the radial error and the rotation angle error when the machine is manipulated to move in circular traces. Based on the measured circular error, a combination of Fourier components is chosen to represent the systematic form error that fluctuates in the radial direction. The typical motion errors represented by the corresponding Fourier components can thus be identified. The values for machine compensation can be calculated and adjusted until the desired results are achieved.

Improved iterative pose estimation algorithm using three-dimensional feature points

In a real-time vision navigation system, an accurate and fast convergent pose estimation algorithm is required for the video guidance sensor. The orthogonal iteration (OI) algorithm is fast and globally convergent, but its results have a large translation error at a close range, and sometimes it fails to give a correct rotation matrix when the data are severely corrupted, when using the 3-D feature points. When the rotation matrix solution in the OI algorithm has been refined, an efficient pose estimation algorithm is derived. Simulation of the improved algorithm shows that the rotation matrix is always proper, which in turn improves the accuracy of the translation vector. The noise resistance and the outlier tolerance are enhanced by using the improved algorithm. The two algorithms are applied to our experimental system for an unmanned vehicle rendezvous and docking simulation separately. The comparison experiments show that the relative distance error is less than 0.28% from 1.5 to 5 m, and the rotation angle error is within ±0.7 deg in 5 m using the improved algorithm. These are better than the results using the OI algorithm.

Effect of Nonlinearity by the Amplitude Variation in coherent transmission in Laser Heterodyne Interferometric

To reduce the nonlinearity of nanometer measurement in laser heterodyne interferometric, the influence mechanics of the amplitude variation in coherent transmission upon nonlinearity must be confirmed. Based on the mechanics of nonlinearity, the models about how first-harmonic and second-harmonic nonlinearity caused by the amplitude variation in coherent transmission are proposed. The emulation result shows that different amplitude between measurement arm and reference arm increases the first-harmonic nonlinearity when laser beams nonorthogonality errors exist, but it doesn't change the relationship between nonlinearity and half wavelength. When the rotation angle error β of polarizing beam splitter (PBS) exists, amplitude variation only affects the first-harmonic nonlinearity. With a constant rotation angle of PBS β = 4°, when the amplitude factor of measurement arm reduces from 1 to 0.6, the nonlinearity increases from 0.25 nm to 3.81 nm, and the nonlinearity is simple superposition of first-harmonic and second-harmonic. Theoretic analysis and emulation show that the reduction of amplitude variation in coherent transmission can reduce influence on nonlinearity.

SEST: A new error separation technique for ultra-high precision roundness measurement

In order to further improve the rotation accuracy of ultraprecision roundness measuring instruments, a new single-step rotation error separation technique (SEST) is proposed to accurately separate instrument spindle rotation error and workpiece roundness error. This is done by first selecting an appropriate rotation angle and rotating the workpiece through a small angle with respect to the instrument spindle, and then measuring mixed errors A(n) and B(n) including workpiece error g(θ) and spindle rotation error z(θ) before and after rotation, and finally achieving accurate separation of z(θ) and g(θ) through Fast Fourier Transformation and harmonic analysis. Theoretical analysis and simulation results indicate that the signals in the harmonic range 1–100 upr can be totally separated from the wide range of harmonics measured when rotation angle error Δα < 0.01° is achieved by optimizing the rotation angle α. In comparison with the multi-step separation technique commonly used in roundness measuring instruments, SEST can be used to totally eliminate any harmonics singularity in the range of 1–100 upr and to make the error separation system very simple, shorten the separation process and reduce the separation time.

Registration of electronic portal images for patient set-up verification

Images acquired from an electronic portal imaging device are aligned with digitally reconstructed radiographs (DRRs) or other portal images to verify patient positioning during radiation therapy. Most of the currently available computer aided registration methods are based on the manual placement of corresponding landmarks. The purpose of the paper is twofold: (a) the establishment of a methodology for patient set-up verification during radiotherapy based on the registration of electronic portal images, and (b) the evaluation of the proposed methodology in a clinical environment. The estimation of set-up errors, using the proposed methodology, can be accomplished by matching the portal image of the current fraction of the treatment with the portal image of the baseline treatment (reference portal image) using a nearly automated technique. The proposed registration method is tested on a number of phantom data as well as on data from four patients. The phantom data included portal images that corresponded to various positions of the phantom on the treatment couch. For each patient, a set of 30 portal images was used. For the phantom data (for both transverse and lateral portal images), the maximum absolute deviations of the translational shifts were within 1.5 mm, whereas the in-plane rotation angle error was less than 0.5°. The two-way Anova revealed no statistical significant variability both within observer and between-observer measurements (P > 0.05). For the patient data, the mean values obtained with manual and the proposed registration methods were within 0.5 mm. In conclusion, the proposed registration method has been incorporated within a system, called ESTERR-PRO. Its image registration capability achieves high accuracy and both intra- and inter-user reproducibility. The system is fully operational within the Radiotherapy Department of ‘HYGEIA’ Hospital in Athens and it could be easily installed in any other clinical environment since it requires standardized hardware specifications and minimal human intervention.

A study on the Hourglass Worm Gearing whose Wheel has the Helical Teeth. (2nd Report).

The authors proposed the hourglass worm gearing with helical Involute gear wheel, and made the numerical simulation and the experiment and confirmed the usefulness of the proposed gearing in the 1st report. The authors tryed to get the initial tooth contact mark at any point on the middle plane on this worm gearing. The authors tryed to analyze the contact marks appears on the wheel tooth, when the both teeth were attached with each other during the rotation of the gearing. This contact marks are so colled the moving tooth contact. The authors developed the soft wear of this moving tooth contact containing the cutting and the assembling errors. This soft wear can also analyze the rotation angle errors.

Analysis of camera movement errors in vision-based vehicle tracking

When a camera is used to provide the navigational parameters in autonomous vehicle operations, it is subjected to unexpected movements or vibrations of the mounting platform. This paper presents a framework for analyzing the effect of uncontrollable camera movements on the navigational parameters, in particular on the range and-heading angle in vision-based vehicle tracking. The noise introduced by the platform movements is modeled in two ways: camera noise approach and image noise approach. The parameter space of the camera is divided into a controllable subspace consisting of its height and depression angle, and an uncontrollable subspace consisting of the tracked object coordinates and rotation angle errors. A consistent detectable region is then obtained such that the tracked object is always seen by the camera. Based on this region, a reliable region consisting of no singularity points is established so that the range error does not become infinity. The optimum parameters of the controllable subspace with respect to the uncontrollable subspace are found by employing two estimation schemes: (a) the mini-max estimator to provide the worst case effect, and (b) the minimum-mean-square estimator to provide the average or overall effect. From the results obtained, it is shown how an optimum imaging geometry of a monocular vision-based tracking system can be designed in order to satisfy prescribed levels of range and heading angle errors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High‐precision t1 imaging method for magnetic resonance imaging

AbstractIt is expected in magnetic resonance imaging (MRI) that the measurement of the longitudinal relaxation time (T1) will be useful in the diagnosis of cancer and in the tissue characterization. The present problem in this regard is the deterioration of the accuracy due to the various factors such as the rotation angle error of 180 deg pulse and the finite repetition time for imaging.From such a viewpcint, this paper derived an expression for the signal intensity for the inversion recovery image (IR image) considering those factors, and it is shown that a highly accurate T1 image with small error can be constructed by the proposed method from at least three images with different inversion times. Then a simplified method is proposed which can derive analytically the T1 image from three IR images obtained without using the iterative calculation, by controlling the inversion times so that they form an arithmetic progression. It was verified by a computer simulation that the error in the T1 image due to the forementioned factors can be kept below 1 percent by the proposed method. Using the MRI system, the T1 image as well as the proton density (rH) image are obtained from a copper‐sulfate phantom. The error between the object and the reconstructed image, which has been as large as 7 to 15 percent, is now suppressed to approximately 1 percent by the proposed method. Thus, the accuracy improvement in T1 and rH images is verified.

Tolerance of imperfections in high-energy circular accelerators for polarized protons.

Realistic calculations show that imperfection-spin-resonance strengths {epsilon}{sub imp} can be corrected to {epsilon}{sub imp}{lt}1, at 20 TeV, Superconducting Super Collider (SSC) energy. Statistical analysis agrees well with the numerical calculation. The polarized proton must be accelerated through overlapping intrinsic and imperfection resonances. We found a correlation between the tolerable strengths of intrinsic and imperfection resonances {epsilon}{sub int} and {epsilon}{sub imp}, that is, at smaller {epsilon}{sub int}, the tolerable {epsilon}{sub imp} becomes larger, and vice versa. To obtain a larger tolerable {epsilon}{sub imp}, we suggest that the number of snakes should be chosen according to {ital N}{sub {ital S}}{ge}5{epsilon}{sub int}. When a large number of snakes is used in the accelerator, the tolerable deviation of the spin rotational angle from 180{degree} for each snake becomes more stringent. The error in the spin rotation angle gives rise to (1) an equivalent picket-fence imperfection resonance {epsilon}{sub imp}{sup eq} and (2) an energy-dependent spin tune {nu}{sub {ital s}}. Both of these effects may cause depolarization. Further, when the snake axis is not properly arranged, the spin tune deviates from half-integer. In this case, depolarization may arise from the snake resonances. Our analysis indicates that acceleration of polarized protons in the SSC is technically feasiblemore » if care is taken in constructing the snakes.« less

Method of pattern positioning for automatic verification of seal imprint

AbstractIn automatic computer verification of seal imprints accurate positioning of an examined seal imprint over a registered imprint is of great importance. This paper proposes a method which positions an examined seal imprint in relation to a parallel shift and rotation by using the centroid of its frame figure and the pixels on a circle of a certain radius from the centroid. Since this method achieves positioning by using local features of the examined seal imprint, rapid positioning is possible. In the presence of small defects in the imprint frame this method has the advantage that the centroid of the seal imprint is accurately obtained and is not affected by distortion of the imprint frame. In a positioning experiment based on this method 240 actual seal imprints were used. All imprints were positioned within a ±0.1‐mm parallel shift error and more than 99% of the seal imprints were positioned within ±1.76° rotation angle errors. A verification experiment was conducted using a seal imprint verification system which incorporated the principles of this method. As a result, the verification error which was caused by the positioning error was found to be 0.83%. The experimental results show that the proposed positioning method is efficient for automatic verification of seal imprints.