Analyse and Research on Motion Control for Helical CT Scanner

There are two motors used in the studied ocean winch, a reel motor and a lead screw motor. This paper focuses on the synchronization control of the two motors. Firstly, the mathematical model of the winch hydraulic transmission system is established, and the approximate relation between the model parameters and the cable storage state is deduced by using interpolation method. Then, combined with the variation rule of the model parameters, an adaptive IMC-PI(internal model control proportional-integral) regulator is designed to control the speed of the reel motor. The parameters of the adaptive IMC-PI regulator are adjusted according to the cable storage state on the reel. The characteristics of master-slave control and cross-coupling control are analyzed, and a new master-slave cross-coupling control method applicable for dual-motor synchronization control is proposed. The new method is realized on the basis of master-slave control. In the dual-motor master-slave cross-coupling synchronization control system, the synchronization angle error is fed back to the master motor control loop, so that the system has perfect synchronization control performance during start-up and running under disturbance. Finally, the validities of the proposed methods are verified by several simulation results.

The drive system of shearer traction unit is affected by complex load interference and system structure, which results in the problem of unbalanced power of dual-motor of shearer traction unit. A new type of dual-motor frequency conversion control system for shearer traction unit with “common rectification and dual inverters” is designed. And a dual-motor power balance control method based on particle swarm optimization torque cross-coupled control is proposed. The new frequency conversion control system adopts a parallel structure of two inverter circuits with a common DC bus. Particle swarm optimization is used to optimize the PID control parameters of torque cross-coupling control, which solves the problem that it is difficult to gain optimal PID parameters. The control model is established using Matlab/Simulink simulation software. The proposed control method and the master-slave control method are compared by simulation. The results show that the control effect of proposed control method is better synchromization and power balance effect than the master-slave control method. The proposed control method is applied to dual-motor control of shearer traction unit for experimental verification. The results indicate that the proposed power balance control method realizes that the output torque ratio of dual-motor is between 0.9 and 1.1.

The purpose of this research was to develop a control method that would provide an operator with a noticeable and reasonable sense of reaction force during slow grasping of a soft object. We examined a master-slave control system for a teleoperation construction robot comprised of two joysticks as the master that are used to manipulate the object from a remote location, and an excavator with four degrees of freedom consisting of a fork glove, swing, boom, and arm as the slave. In remote control systems, the operator must feel a reasonable sense of force from the fork glove feedback. We previously proposed a variable-gain velocity control system but found that the reaction force was insufficient and often undetectable to operators' sensory receptors in the initial stage of the grasping task, and the reaction force did not appear as a stepwise relation to the increased driving force when grasping a foam block at a slow speed. Based on these earlier problems, we proposed an improved method that provides a noticeable torque and variable gain that changes with the hardness of the task object. Its effectiveness was verified by a concrete block, tire, and sponge foam block grasping experiment.

Temperature field of planar laser cladding with length direction, width direction and helical scanning path were simulated and analysed. Temperature distribution could be effected significantly by the laser scanning path. For short-path scanning, heat was concentrated in the local area, resulting in larger (/smaller) temperature gradient in the length (/width) direction of the substrate. However, such characteristics of long-path scanning were on the contrary. By comparison, the heat affected zone (HAZ) of the substrate with helical scanning mode was the smallest and its temperature fluctuations were more dispersed.

This paper presents a synchronous control method for multiple-axis servo-systems aimed at the synchronization and cooperation of all axes. An optimum synchronous time-varying controller is presented in terms of a time-varying performance index and it is given by solving a time-varying Ricatti differential equation-given, where the position synchronization can be realized for the circular path and the combination path that consists of the straight-line path and the circular path. The control method proposed in this paper is applied to an X-Y table, which is a two-axis system. The proposed control method is demonstrated experimentally in a two-axis system to make the conventional independent control that is conducted separately, for each axis develop both the tracking precision for reference path and the reduction of system fluctuation for disturbance.

As a large-scale special lifting equipment, the positioning error of polar crane in nuclear power plant (abbreviated as polar crane) should be less than 5 mm. The operation control of crane traveling mechanism is the key technology to improve the positioning accuracy of polar crane. Firstly, based on the principle of virtual work, the dynamic model of polar crane is established. Secondly, a synchronous control method of crane traveling mechanism based on the combination of synchronous relative coupling control and a novel nonsingular fast terminal sliding mode control is proposed. Finally, the horizontal wheel-rail gap and lateral force of horizontal guide device are taken as evaluation indexes, working process and influence mechanism on positioning accuracy of the control method under the influence of the drive response delay of crane traveling mechanism are analyzed. This paper provides valuable reference for improving the positioning accuracy and robustness of polar crane.

This paper presents the synchronous efficiency of two synchronous control methods based on a PID controller for the model of two electric motors with variable load. The two synchronization methods used are the Master-Slave method and the Cross-Coupling method. First, a mathematical model of the motor, load variation, and system is established. Then, a combine with Motor parameters throughs identification to conduct system simulation. Simultaneously, the design and synchronous control for this two-motors system were also carried out. Moreover, the characteristics and properties of the Master-Slave and Cross-Coupling synchronization methods are studied and analyzed. The Master-Slave method uses a sample Motor and is followed by a dependent Motor that is operated on the signal of the sample Motor. The Cross-Coupling method is based on the signal error of each motor compared to the desired value and the error between the motors. Finally, the evaluation of the effectiveness of these two methods is made based on the results obtained from simulation and experiment. From simulation and experimental results, it shows that the Master-Slave and Cross-Coupling methods help to solve phase synchronization and error. The difference between the two motors, the Cross-Coupling method also solves the problem of the response time of the two motors and the error at the start of the two motors simply.KeywordsDual motor systemMaster-slaveCross-couplingSynchronization controlPID controller

In oil and gas drilling engineering, the anti-phase synchronization of two co-rotating rotors in a tri-motor vibration system is easy to implement owing to its inherent coupling characteristics, which can lead to the exciting force generated by the vibrating system being very small. Thus, an adaptive back-stepping control strategy is proposed to apply in a tri-motor vibrating system and improve the processing capacity of drilling fluid shaker screens. The algorithm developed in this paper is that a complex higher-order nonlinear system is simplified into lower-order subsystems by the adaptive back-stepping control theory, and then the adaptive law for varying load torque is derived by combining with the adaptive theory to regulate the velocity of motors in a closed loop. Firstly, a dynamical model to describe the tri-motor vibration system is established, and the dynamical equations of the vibrating system are derived based on the Lagrange equation. Then, the speed error controller and the phase difference error controller are designed by combining the adaptive back-stepping control algorithm with the master–slave control (MSC) structure. According to Barbalat’s lemma, the stability of the control system is analyzed to verify the feasibility of the control method. Finally, the dynamical equations of the vibrating system are used to establish an electromechanical coupling control model of a tri-motor driven planar system through the Runge–Kutta method, and it verified the reliability of the control strategy, the robustness, and the stability of the control system, respectively, and intuitively revealed the synchronization characteristics of tri-motor vibration control system. The results demonstrate the phase difference among the three motors can be accurately stabilized at zero by a phase synchronization control strategy based on the adaptive back-stepping control method, and the method is simple and fast-speed and the control system has better robustness.

With the development of ATO (Automatic Train Operation) system for heavy-haul trains, advanced control methods to ensure the safe and stable operation of the train have become an urgent demand. To this end, a cascade control method based on MPC-PI (model predictive control and proportional integral) control is proposed. A multi-particle dynamic model of heavy-haul trains is established, and then the model is linearized for control algorithm design. In this cascade control method, the outer loop adopts MPC with large sampling time, and the optimization objectives consist of in-train forces, energy consumption and speed tracking error. The MPC control is formulated as QP (Quadratic Programming) problem, the output of which is used as the initial input of the inner loop. The inner loop adopts PI control with small sampling time, and adjusts the actual train control output in real time for the speed tracking error. The simulation results of 20,000 tons heavy-haul train show that the proposed method has better robustness and anti-interference than MPC and PI control separately. The optimization objective function is formulated with weighted coupler force and energy consumption, and the simulation results are compared with different sets of weights, which prove the effectiveness of the proposed method.

In order to solve the attitude synchronization control problem of an on-orbit servicing spacecraft autonomously docking to a tumbling satellite with the unknown bounded disturbances and system uncertainties, a fast terminal sliding mode control law is presented in this paper. The most important contribution of this paper is to design an attitude synchronization control law, which will be realized by the terminal sliding mode control method, for a servicing spacecraft autonomously docking to a freely tumbling satellite in space. First of all, the model of relative attitude dynamics is derived from the attitude dynamics of servicing spacecraft and tumbling satellite. Then, the relative attitude dynamic model is converted to the normal formation to apply the control method of fast terminal sliding mode. Furthermore, a fast terminal sliding mode control law for attitude synchronization is designed based on the normal formation of relative attitude dynamic model. During the design process of the control law, the measurement errors and parameter variations are also considered. Finally, several numerical simulations are conducted to verify the designed attitude synchronization control law, and the results verified the effectiveness of the designed control law. Moreover, it's robustness to the unknown bounded disturbances, system uncertainties and measurement errors has also been demonstrated.

Multi-slice CT (MCT) is one of the most recent technical advancements in computed tomography. MCT offers high volume coverage, faster scan speed, and reduced x-ray tube loading. When combined with the helical scan mode, MCT provides even higher volume coverage as a result of the elimination of the inter-scan delays. Similar to the single slice CT, the projection data collected in MCT is inherently inconsistent. To combat projection inconsistency, many image reconstruction algorithms were investigated and developed. Recent studies have shown, however, that the image quality of MCT can be significantly degraded when the data is collected in a tilted helical mode. The degradation can be so severe that it is unacceptable for routine clinical usage. In this paper, we present a detailed investigation to show that the root cause of the image quality degradation is the deviation of the reconstruction iso-center from the gantry iso-center. An analytical model is derived to establish a quantitative relationship between the iso0center shift and other system parameters. The model serves as the mathematical basis for the derivation of a frequency-domain correction algorithm. Detailed performance evaluation is provided in terms of spatial resolution, noise, computational efficiency, and image artifacts.

Through the double cylinder synchronous lifting system in-depth study presents a master-slave control method and the single neuron PID control strategy for controlling synchronization accuracy. Simulation results show that this method can achieve higher precision synchronization control.

A Monte Carlo (MC) modeling of single axial and helical CT scan modes has been developed to compute single and accumulated dose distributions. The radiation emission characteristics of an MDCT scanner has been modeled and used to evaluate the dose deposition in infinitely long head and body PMMA phantoms. The simulated accumulated dose distributions determined the approach to equilibrium function, H(L). From these curves, dose-related information was calculated for different head and body clinical protocols. The PENELOPE/penEasy package has been used to model the single axial and helical procedures and the radiation transport of photons and electrons in the phantoms. The bowtie filters, heel effect, focal-spot angle, and fan-beam geometry were incorporated. Head and body protocols with different pitch values were modeled for x-ray spectra corresponding to 80, 100, 120, and 140kV. The analytical formulation for the single dose distributions and experimental measurements of single and accumulated dose distributions were employed to validate the MC results. The experimental dose distributions were measured with OSLDs and a thimble ion chamber inserted into PMMA phantoms. Also, the experimental values of the along the center and peripheral axes of the CTDI phantom served to calibrate the simulated single and accumulated dose distributions. The match of the simulated dose distributions with the reference data supports the correct modeling of the heel effect and the radiation transport in the phantom material reflected in the tails of the dose distributions. The validation of the x-ray source model was done comparing the CTDI ratios between simulated, measured and CTDosimetry data. The average difference of these ratios for head and body protocols between the simulated and measured data was in the range of 13-17% and between simulated and CTDosimetry data varied 10-13%. The distributions of simulated doses and those measured with the thimble ion chamber are compatible within 3%. In this study, it was demonstrated that the efficiencies of the measurements in head phantoms with nT=20mm and 120kV are 80.6% and 87.8% at central and peripheral axes, respectively. In the body phantoms with =40mm and 120kV, the efficiencies are 56.5% and 86.2% at central and peripheral axes, respectively. In general terms, the clinical parameters such as pitch, beam intensity, and voltage affect the Deq values with the increase of the pitch decreasing the Deq and the beam intensity and the voltage increasing its value. The H(L) function does not change with the pitch values, but depends on the phantom axis (central or peripheral). The computation of the pitch-equilibrium dose product, , evidenced the limitations of the method to determine the dose delivered by a CT scanner. Therefore, quantities derived from the propagate this limitation. The developed MC model shows excellent compatibility with both measurements and literature quantities defined by AAPM Reports 111 and 200. These results demonstrate the robustness and versatility of the proposed modeling method.

The spatial resolution of diagnostic Computed Tomography (CT) has increased substantially, and 3D isotropic sub-millimeter spatial resolution in both axial and helical scan modes is routinely available in the clinic. However, driven by advanced clinical applications, the pursuit for higher spatial resolution and free of aliasing artifacts in diagnostic CT has never stopped. A method to accommodate focal spot wobbling at an arbitrary number of projection views per gantry rotation in CT is presented and evaluated here. The method employs a beta-correction scheme in the row-wise fan-to-parallel rebinning to transform the native cone beam geometry into the cone-parallel geometry under which existing 3D weighted cone beam filtered backprojection algorithms can be utilized for image reconstruction. The experimental evaluation shows that the row-wise fan-to-parallel rebinning with the beta-correction can increase the quantitative in-plane spatial resolution (Modulation Transfer Function) substantially, while the visual spatial resolution can be enhanced significantly. Consequently, the architectural designers of CT scanners are no longer constrained to choosing the number of projection views per rotation determined by gantry geometry. Instead, they can choose the number of projection views per rotation to optimize the trade-offs between in-plane spatial resolution and noise characteristics. Therefore, the presented method is of practical relevance in the architectural design of state-of-the-art diagnostic CT.

Comparison of the Dixon and CTDI dose quantification techniques