Position and orientation estimation with high accuracy based on GPS and encoders for a four-wheel-steering vehicle (4WS) mobile robot is presented. A GPS receiver working in Real-Time Kinematics (RTK) mode can offer c...Position and orientation estimation with high accuracy based on GPS and encoders for a four-wheel-steering vehicle (4WS) mobile robot is presented. A GPS receiver working in Real-Time Kinematics (RTK) mode can offer centimeter-level accuracy for our vehicle. In addition to GPS, the vehicle is equipped with four incremental encoders and two absolute encoders to provide information on wheels for estimation of velocity and sideslip angle of vehicle. The proposed architecture of position and orientation estimation consists of two extended Kalman filters and a processing unit of Runga-Kutta based dead reckoning. The first EKF fuses data from six encoders to estimate the vehicle velocity and the sideslip angle. The second EKF is applied to the estimation of position and orientation based on the measurement from precise RTK GPS data and output from first EKF. To obtain higher accuracy of estimation, an arbitrator is designed to switch between EKF2 and dead reckoning. The results and analysis of experiments are presented to show the effectiveness of the proposed approach. Limitations of the proposed approach and future works are also pointed out and discussed in this paper.展开更多
The counter-rotating type hydroelectric unit, which is composed of the axial flow type tandem runners and the peculiar generator with double rotational armatures, has been proposed. In the unit, the front and the rear...The counter-rotating type hydroelectric unit, which is composed of the axial flow type tandem runners and the peculiar generator with double rotational armatures, has been proposed. In the unit, the front and the rear runners counter-drive the inner and the outer armatures of the generator, respectively. Besides, the flow direction at the rear runner outlet must coincide with the direction at the front runner inlet, because the angular momentum change through the rear runner must coincides with that through the front runner. In this paper, the tandem runners work at on-cam conditions in keeping the induced frequency constant, to provide the hydroelectric unit for the power grid system. The output and the hydraulic efficiency are affected by the adjusting angles of the front and the rear blades. Both optimum angles giving the maximum output or efficiency were presented at the various discharge/head circumstances, accompanying with the turbine performances.展开更多
Vibration behaviors of bogie hunting motion contain key information that dominates the dynamic performance of rail vehicles,in which the eigenvalue of each mode reflects the damping ratio and the natural frequency.Thi...Vibration behaviors of bogie hunting motion contain key information that dominates the dynamic performance of rail vehicles,in which the eigenvalue of each mode reflects the damping ratio and the natural frequency.This paper focuses on the root loci curves of bogie hunting motion,starting from a rigid bogie,then to a bogie with flexible primary suspension.With regard to the rigid bogie,analytical formulas for the eigenvalues,the critical speed as well as the corresponding hunting frequency are derived and verified.While for the flexible bogie,the root loci curves are calculated numerically.The study shows that both free rigid bogie and free wheelset are dynamically unstable at any speed.The critical speed increases with diminished wheel-rail conicity,track gauge,and wheelset and bogie inertia,and with increased wheelbase and wheel radius.The dominating factors such as the stiffness of the primary suspension and the wheel-rail conicity should be optimized for a practical design.The influences of the damping coefficients and the variations of creep coefficients are negligible.The motor suspension affects the root loci curves and the critical speed significantly.Both inappropriate motor suspension design and rigidly suspended motor reduce the critical speed.The increase of critical speed by a motor suspension can only be achieved when the lower natural frequency of the motor-bogie frame-wheelsets system coincides with or is close to the hunting frequency.Special care should be taken for the design of motor suspension,the first is to avoid the decreased damping ratio in a certain speed range below the critical speed and the second is that the variations of parameters should not induce the rapid reduction of the critical speed.The main feature of the present study is that the root loci curves,which are derived as analytical formulas or calculated numerically,are used to study the vibrational behaviors of bogie hunting motion.Both the influencing laws of the dominating parameters and the principles regarding the motor suspension are significant for the stability design of modem railway vehicles which may use innovative structures/materials as well as modem control and monitoring technologies.展开更多
文摘Position and orientation estimation with high accuracy based on GPS and encoders for a four-wheel-steering vehicle (4WS) mobile robot is presented. A GPS receiver working in Real-Time Kinematics (RTK) mode can offer centimeter-level accuracy for our vehicle. In addition to GPS, the vehicle is equipped with four incremental encoders and two absolute encoders to provide information on wheels for estimation of velocity and sideslip angle of vehicle. The proposed architecture of position and orientation estimation consists of two extended Kalman filters and a processing unit of Runga-Kutta based dead reckoning. The first EKF fuses data from six encoders to estimate the vehicle velocity and the sideslip angle. The second EKF is applied to the estimation of position and orientation based on the measurement from precise RTK GPS data and output from first EKF. To obtain higher accuracy of estimation, an arbitrator is designed to switch between EKF2 and dead reckoning. The results and analysis of experiments are presented to show the effectiveness of the proposed approach. Limitations of the proposed approach and future works are also pointed out and discussed in this paper.
文摘The counter-rotating type hydroelectric unit, which is composed of the axial flow type tandem runners and the peculiar generator with double rotational armatures, has been proposed. In the unit, the front and the rear runners counter-drive the inner and the outer armatures of the generator, respectively. Besides, the flow direction at the rear runner outlet must coincide with the direction at the front runner inlet, because the angular momentum change through the rear runner must coincides with that through the front runner. In this paper, the tandem runners work at on-cam conditions in keeping the induced frequency constant, to provide the hydroelectric unit for the power grid system. The output and the hydraulic efficiency are affected by the adjusting angles of the front and the rear blades. Both optimum angles giving the maximum output or efficiency were presented at the various discharge/head circumstances, accompanying with the turbine performances.
基金supported by the National Natural Science Foundation of China(Grant Nos.51805452,and 51935002)the Independent Research Project of State Key Laboratory of Traction Power(Grant No.2020TPL-T02).
文摘Vibration behaviors of bogie hunting motion contain key information that dominates the dynamic performance of rail vehicles,in which the eigenvalue of each mode reflects the damping ratio and the natural frequency.This paper focuses on the root loci curves of bogie hunting motion,starting from a rigid bogie,then to a bogie with flexible primary suspension.With regard to the rigid bogie,analytical formulas for the eigenvalues,the critical speed as well as the corresponding hunting frequency are derived and verified.While for the flexible bogie,the root loci curves are calculated numerically.The study shows that both free rigid bogie and free wheelset are dynamically unstable at any speed.The critical speed increases with diminished wheel-rail conicity,track gauge,and wheelset and bogie inertia,and with increased wheelbase and wheel radius.The dominating factors such as the stiffness of the primary suspension and the wheel-rail conicity should be optimized for a practical design.The influences of the damping coefficients and the variations of creep coefficients are negligible.The motor suspension affects the root loci curves and the critical speed significantly.Both inappropriate motor suspension design and rigidly suspended motor reduce the critical speed.The increase of critical speed by a motor suspension can only be achieved when the lower natural frequency of the motor-bogie frame-wheelsets system coincides with or is close to the hunting frequency.Special care should be taken for the design of motor suspension,the first is to avoid the decreased damping ratio in a certain speed range below the critical speed and the second is that the variations of parameters should not induce the rapid reduction of the critical speed.The main feature of the present study is that the root loci curves,which are derived as analytical formulas or calculated numerically,are used to study the vibrational behaviors of bogie hunting motion.Both the influencing laws of the dominating parameters and the principles regarding the motor suspension are significant for the stability design of modem railway vehicles which may use innovative structures/materials as well as modem control and monitoring technologies.
