Compensation Precision Research Articles

Error Compensation on a NC-Machine Tool Based on Integrated Intelligent Computation

This paper is a study of the application of integrated intelligent computation to solve the problems of error compensation for high-precision a NC machining system. The primary focus is on the development of integrated intelligent computation approach to get an error compensation system which is a dynamic feedback neural network embedded in a NC machine tool. Optimization of error measurement points of a NC machine tool is realized by way of application of error variable attribute reduction on rough set theory. A principal component analysis is used for data compression and feature extraction to reduce the input dimension of a dynamic feedback neural network and reduce training time of the network. Taking advantage of ant colony algorithm on training of a dynamic feedback neural network does the global search so that network can converge to get a global optimum. Positioning error caused in thermal deformation compensation capabilities were tested using industry standard equipment and procedures. The results obtained shows that this approach can effectively improve compensation precision and real time of error compensation on machine tools.

Sensor Compensation Based on Adaptive Ant Colony Neural Networks

In order to improve work stability and measurement accuracy of drilling inclinometer, and overcome the poor stability of Elman networks and lower compensation precision of genetic Elman neural networks, we combined ant colony algorithm and neural networks, using the Adaptive Ant Colony Algorithm that its pheromone evaporation factorand pheromone update strategy adjust adaptively to optimize Elman neural network weights and thresholds, and applied it to drilling inclinometer sensor compensation. Simulation results show that the compensation effect of adaptive ant colony Elman neural networks is better than that of Elman networks and genetic Elman networks, the compensation accuracy is 10-8.

Error Compensation of a NC Machining System Based on a Dynamic Feedback Neural Network

Machining error of a NC machining system is a kind of comprehensive error in dynamically machining process; especially it is of errors with non-linear characteristics. In this paper, we will set up a kind of model of comprehensive errors analysis for a NC machining system and present an error compensation for high-precision a NC machining system by a dynamic feedback neural network embedded in a NC machine tool. The results obtained shows that this approach can effectively improve compensation precision and real time of error compensation on machine tools.

TH‐C‐350‐05: Performance of a Beam Tracking System for Treatment of Moving Targets with Scanned Ion Beams

Purpose: Scanned ion beam therapy of intra‐fractionally moving targets requires motion mitigation to prevent deteriorations of the delivered doses due to interplay. A beam tracking system was developed and experiments with various detectors were performed to assess system performance. Method and Materials: Tracking of moving targets with scanned ion beams requires simultaneous lateral and longitudinal range adaptation of pencil beam positions. Lateral beam tracking is achieved directly with the beam scanning system. Longitudinal tracking is performed with a dedicated energy modulation system consisting of fast, motorized absorber wedges. In experiments with radiographic films, a range telescope, and an array of pin‐point ionization chambers in a water phantom, the precision of lateral, longitudinal, and 3D motion compensation was measured. Motion was induced laterally by a sliding table and longitudinally by ramp‐shaped absorbers. Motion detection was performed with a laser‐triangulation sensor. Experimental tracking data were compared to results of measurements with stationary detector systems. Films were analyzed with respect to geometrical shape as well as mean, minimum, and maximum response level within the target region. Ionization chamber data were analyzed for different volumes of the setup. Analysis of range telescope data focused on Bragg‐peak shapes and ranges. Results: Film analysis yielded conservation of geometrical shape and responses (mean±SD, minimum, maximum) of (0.276±0.010, 0.241, 0.288) and (0.275±0.007, 0.252, 0.284) for stationary irradiation and tracking respectively. Within the target volume, ionization chamber data with beam tracking deviated from stationary irradiation by 0.3 ± 1.5% with −2.7% minimum and 3.7% maximum deviation. The Bragg peak range for tracking deviated by less than 0.25 mm water‐equivalent from the stationary reference. Conclusion: The tracking system for scanned ion beams successfully restored dose distributions for moving targets by adapting individual Bragg peaks during irradiations in quasi real time.Research sponsored in part by Siemens Healthcare, Particle Therapy.

Designing dispersion-compensating photonic-crystal fibers using a genetic algorithm

A genetic algorithm is combined with a fully vectorial finite-element solver to design photonic-crystal fibers (PCFs) for a broadband dispersion compensation in a generic stretcher–compressor system of an ytterbium fiber laser. Two types of PCFs are compared in terms of their dispersion-compensation capability, optical nonlinearity, and confinement loss. Fibers of the first type are standard PCFs where a solid core is surrounded by a triangular uniform lattice of identical air-holes. In PCFs of the second type, the solid core is surrounded by a dual-scale cladding, where the inner part comprises air-holes of different diameters, while the outer cladding consists of large-diameter air-holes. Second-type PCFs are shown to provide a much more accurate dispersion compensation. The influence of fiber-fabrication tolerances on the precision of dispersion compensation in short-pulse fiber laser systems is examined.

Simulations to design an online motion compensation system for scanned particle beams

Respiration-induced target motion is a major problem in intensity-modulated radiation therapy. Beam segments are delivered serially to form the total dose distribution. In the presence of motion, the spatial relation between dose deposition from different segments will be lost. Usually, this results in over- and underdosage. Besides such interplay effects between target motion and dynamic beam delivery as known from photon therapy, changes in internal density have an impact on delivered dose for intensity-modulated charged particle therapy. In this study, we have analysed interplay effects between raster scanned carbon ion beams and target motion. Furthermore, the potential of an online motion strategy was assessed in several simulations. An extended version of the clinical treatment planning software was used to calculate dose distributions to moving targets with and without motion compensation. For motion compensation, each individual ion pencil beam tracked the planned target position in the lateral as well as longitudinal direction. Target translations and rotations, including changes in internal density, were simulated. Target motion simulating breathing resulted in severe degradation of delivered dose distributions. For example, for motion amplitudes of ±15 mm, only 47% of the target volume received 80% of the planned dose. Unpredictability of resulting dose distributions was demonstrated by varying motion parameters. On the other hand, motion compensation allowed for dose distributions for moving targets comparable to those for static targets. Even limited compensation precision (standard deviation ∼2 mm), introduced to simulate possible limitations of real-time target tracking, resulted in less than 3% loss in dose homogeneity.

Kalman filtering based rate-constrained motion estimation for very low bit rate video coding

The rate-constrained (R-D) motion estimation techniques have been presented to improve the conventional block-matching algorithm by using a joint rate and distortion criterion. This paper presents two motion estimation algorithms using Kalman filter to further enhance the performance of the conventional R-D motion estimation at a relative low computational cost. The Kalman filter exploits the correlation of block motion to achieve higher precision of motion estimation and compensation. In the first algorithm, the Kalman filter is utilized as a postprocessing to raise the motion compensation accuracy of the conventional R-D motion estimation. In the second algorithm, the Kalman filter is embedded into the optimization process of R-D motion estimation by defining a new R-D criterion. It further improves the rate-distortion performance significantly.

Rate-constrained motion estimation using Kalman filter

The rate-constrained (R–D) motion estimation techniques have been presented to improve the conventional block-matching algorithm by using a joint rate and distortion criterion. This paper presents a new motion estimation algorithm using Kalman filter to improve the performance of the conventional R–D motion estimation at a relatively low computational cost. The Kalman filter exploits the correlation of block motion to achieve higher precision of motion estimation and compensation. In the proposed algorithm, the Kalman filter is embedded into the optimization process of R–D motion estimation by defining a new R–D criterion. Simulation results show that the new algorithm improves the rate–distortion performance significantly.

Increasing registration precision for liver movement with respiration using electromagnetic tracking

Respiratory motion of the liver is a major concern when trying to precisely target liver lesions. The purpose of this study is to increase the accuracy of an image-guided system for abdominal interventions by tracking multiple needles within the liver and selecting the time stamp that provides the smallest registration error throughout the whole respiratory cycle. Phantom and swine studies have been completed. The results indicate that the method presented can increase the precision of registration compensation compared with respiratory gating and non-gating methods.

Pressure compensation method of under water hydraulic system with hydraulic power unit being under atmospheric circumstance and pressure compensated valve

Based on the analysis of the-state-of-the-art of pressure compensation of underwater hydraulic systems (UHSs), a new method of pressure compensation of UHSs, whose hydraulic power unit is in the atmospheric circumstance, is proposed. And a pilot-operated relief valve with pressure compensation is realized. The pressure compensation precision is guaranteed by direct detection. Its dynamic performance and stability are improved by a dynamic feedback. Theoretical study, simulation and experiment show that the pilot-operated relief valve with pressure compensation has a fine property of tracking underwater ambient pressure and meet the requirement of underwater ambient pressure compensation.

An algorithm using genetic programming for the compensation of nonlinear distortion based on wiener system model

In this paper we presented an iteration algorithm using genetic programming (GP) to get the Wiener model of a nonlinear system and then to compensate the nonlinear distortion. The GP is used to identify the linear time-invariant (LTI) part and memory less nonlinear (MLNL) part of the Wiener model of the object system. By means of iteration, the identification precision will be improved gradually with the iteration steps. In order to compensate the non linearity a distortion compensation function (DCF) will be estimated also by means of GP. If the object system can be well described using Wiener model, this algorithm converges. The experiment results show that the compensation precision is fairly high.

Operator method for estimating the precision of distortion compensation by adaptive correction

An operator method for estimating the effectiveness of adaptive mirrors is proposed and developed. This method yields a simple mathematical expression for the minimum residual error in the compensation of wavefront distortions. The expression makes it possible to estimate rapidly the precision of distortion compensation in the case of any adaptive mirror and any wavefront without recourse to a computer. The effectiveness of the method is demonstrated by the example of a bimorph adaptive mirror.

Calculation of the thermal compensation of Hall transducers with thin indium antimonide films

1. In feeding indium antimonide thin-film Hall transducers from sources with a small internal resistance it is advisable to use a series thermal compensation circuit consisting of resistances which vary linearly with temperature. 2. A thermal compensation precision suitable for practical purposes over an adequately wide temperature range can be obtained with thermal resistances which have positive and negative coefficients. 3. The thermal compensation circuit is very simple and can be easily calculated. 4. The power loss in the thermal compensation circuit is very small. 5. The maximum residual error mmax can be reduced substantially by selecting a thermal compensation material with a temperature coefficient ασ for which function mmax=f(αs) intersects the axis of abscissas (for instance, in the case under consideration ασ=−1%/°C). The required values of ασ and\(r_{\delta _{20} } \) can be easily obtained by combining thermistors with temperature-stable resistances according to the technique described in [4, 5].