A calibration scheme under spherical coordinates is described for a magnetic tracker used in VR (virtual reality) system. A look up table containing data of tracked values for certain positions in the working space, ...A calibration scheme under spherical coordinates is described for a magnetic tracker used in VR (virtual reality) system. A look up table containing data of tracked values for certain positions in the working space, spe cified in spherical coordinates, is generated first, which is then used to calibrate the tracking results by a two dimensional interpolation. The scheme can effectively correct the static errors in the magnetic tracking system. The employment of spherical coordinates significantly reduces the calculation complexity in calibration.展开更多
This paper presents a flexible and high speed digital scan converter (DSC) with the ability to handle high frequency ultrasound imaging in real-time. The characteristics in imaging system such as focus length of trans...This paper presents a flexible and high speed digital scan converter (DSC) with the ability to handle high frequency ultrasound imaging in real-time. The characteristics in imaging system such as focus length of transducer, the swing radius and sampling length etc. could be changed easily in compliance with the researcher's application based on this flexible digital scan converter. Linear interpolation is employed to achieve the coordinate transformations algorithm. Custom-built software is programmed to preliminarily handle the algorithm according to different ultrasound imaging applications. High performance FPGA will implement high speed interpolation calculation based on the preliminary data which are stored in the DDR2 SDRAM from the software. 64 bit 66 MHz PCI is employed to accomplish high speed data transmission. Experiment has shown that more than 500 frame rate could be achieved based on this high speed digital scan converter. The designed flexible and high speed digital scan converter could be used in current FPGA based high frequency ultrasound imaging system.展开更多
True proportional navigation(TPN) guidance law is widely used for exoatmospheric interception, for its robustness and ease of implementation. The performance of TPN against nonmaneuvering target or the maneuvering tar...True proportional navigation(TPN) guidance law is widely used for exoatmospheric interception, for its robustness and ease of implementation. The performance of TPN against nonmaneuvering target or the maneuvering target with a specific acceleration had been analyzed before. However, the obtained results are not suitable for the realistic exoatmospheric interception scenario,since the target may maneuver along an arbitrary direction with an arbitrary but upper-bounded acceleration in the threedimensional(3 D) space, which is the so-called "true-arbitrarily maneuvering target" in this paper. With the help of the line-ofsight(LOS) rotation coordinate system, the performance of 3 D TPN against the true-arbitrarily maneuvering target is thoroughly analyzed using the Lyapunov-like approach. The upper-bound of the 3 D LOS rate is obtained, and so is that of the commanded acceleration of 3 D TPN. After that, the capture region of 3 D TPN is presented on the initial relative velocity plane. The nonlinear3 D relative kinematics between the interceptor and the target is taken into full account. Finally, the new theoretical findings are demonstrated by numerical simulations.展开更多
文摘A calibration scheme under spherical coordinates is described for a magnetic tracker used in VR (virtual reality) system. A look up table containing data of tracked values for certain positions in the working space, spe cified in spherical coordinates, is generated first, which is then used to calibrate the tracking results by a two dimensional interpolation. The scheme can effectively correct the static errors in the magnetic tracking system. The employment of spherical coordinates significantly reduces the calculation complexity in calibration.
文摘This paper presents a flexible and high speed digital scan converter (DSC) with the ability to handle high frequency ultrasound imaging in real-time. The characteristics in imaging system such as focus length of transducer, the swing radius and sampling length etc. could be changed easily in compliance with the researcher's application based on this flexible digital scan converter. Linear interpolation is employed to achieve the coordinate transformations algorithm. Custom-built software is programmed to preliminarily handle the algorithm according to different ultrasound imaging applications. High performance FPGA will implement high speed interpolation calculation based on the preliminary data which are stored in the DDR2 SDRAM from the software. 64 bit 66 MHz PCI is employed to accomplish high speed data transmission. Experiment has shown that more than 500 frame rate could be achieved based on this high speed digital scan converter. The designed flexible and high speed digital scan converter could be used in current FPGA based high frequency ultrasound imaging system.
基金supported by the National Natural Science Foundation of China(Grant Nos.61690210 and 61690213)
文摘True proportional navigation(TPN) guidance law is widely used for exoatmospheric interception, for its robustness and ease of implementation. The performance of TPN against nonmaneuvering target or the maneuvering target with a specific acceleration had been analyzed before. However, the obtained results are not suitable for the realistic exoatmospheric interception scenario,since the target may maneuver along an arbitrary direction with an arbitrary but upper-bounded acceleration in the threedimensional(3 D) space, which is the so-called "true-arbitrarily maneuvering target" in this paper. With the help of the line-ofsight(LOS) rotation coordinate system, the performance of 3 D TPN against the true-arbitrarily maneuvering target is thoroughly analyzed using the Lyapunov-like approach. The upper-bound of the 3 D LOS rate is obtained, and so is that of the commanded acceleration of 3 D TPN. After that, the capture region of 3 D TPN is presented on the initial relative velocity plane. The nonlinear3 D relative kinematics between the interceptor and the target is taken into full account. Finally, the new theoretical findings are demonstrated by numerical simulations.
