Degrees of Freedom Control through Three Electromagnets and Three Linear Induction Motors
Configuration that the mover has three electromagnets and three linear induction motor (LIM) has been proposed for contactless flexible conveyance system. Hybrid electromagnet that uses permanent magnet can let power consumption converge to zero in steady state, and its stator becomes simple because the combination of three LIM’s is used for two-dimensional drive. The normal attractive force of LIM can increase the carrying capacity of the mover, although it can be also disturbance force for the stabilization of the magnetic levitation system. Authors have experimentally confirmed that the proposed configuration can realize six-degrees of freedom control of the mover. Position sensing for the closed loop control of two-dimensional linear drive is difficult: one possible approach based on visual sensing combined with dual sample-rate digital observer is proposed and discussed.
4 Poles 3 Degrees of Freedom Magnetic Levitation Control and its Coordination with Two-Dimensional Linear Motor
Electromagnetic suspension (EMS) has been widely used in many industrial fields because of various advantages in practical use. The U-type magnets are often used to generate the levitation force in the EMS system. This conventional electromagnet, however, can only control one degree-offreedom. It cannot construct a levitation system solely by itself. A 4-pole type yoke hybrid electromagnet is proposed instead of the usual U-type magnet and its magnetic levitation control is studied in this paper. The basic structure and characteristics of the proposed magnet are described, and the control systems are designed. The semi-zero-power controller, with a disturbance observer, is proposed to improve the performance of the control system. Furthermore, the combination with the linear motor is discussed.
Monte Carlo Study of the Effect of Backscatter Materail Thickness on 99 mTc Source Response in Single Photon Emission Computed Tomography
Introduction SPECT projections are contaminated by scatter radiation, resulting in reduced image contrast and quantitative errors. Backscatter constitutes a major part of the scatter contamination in lower energy windows. The current study is an evaluation of the effect of backscatter material on FWHM and image quality investigated by Monte Carlo simulation. Materials and Methods SIMIND program was used for simulation of a Siemen’s dual-head variable angle scintillation gamma camera. Planar and SPECT scanning of a 99m Tc source and a Jaszczak phantom for varying thicknesses of Perspex slabs, as a backscatter media, were analyzed using the photopeak and scatter windows. Simulated planar images and reconstructed tomographic images were evaluated qualitatively, by two nuclear medicine specialists, and quantitatively, by Structural Similarity (SSIM) Index. Results In the 99m Tc photopeak window, no significant change in total counts due to backscatter material was measured. In the scatter windows, scattering was overestimated compared with a simulated backscatter free SPECT system. For instance, at a thickness of 10 cm, total counts of a 99m Tc source detected in the 72 keV windows eventually doubled with increasing backscatter material, compared with the situation without backscatter material. The backscatter contribution plateaued when more than 7 cm of scatter material was placed but there were optimized results for a backscatter thickness of 4.5 cm. Better image quality for the thickness was confirmed by the results of eye interpretation and also by SSIM algorithm. Conclusion Backscatter should be taken into account, particularly in model-based scatter correction methods in SPECT for an accurate simulation system optimization.