A jumping mechanism can be an efficient mode of motion for small robots to overcome large obstacles on the ground and rough terrain. In this paper, we present a 7 g prototype of locust-inspired jumping mechanism that ...A jumping mechanism can be an efficient mode of motion for small robots to overcome large obstacles on the ground and rough terrain. In this paper, we present a 7 g prototype of locust-inspired jumping mechanism that uses springs, wire, reduction gears, and a motor as the actuation components. The leg structure and muscles of a locust or grasshopper were mimicked using springs and wire, springs for passive extensor muscles, and a wire as a flexor muscle. A small motor was used to slowly charge the spring through a lever and gear system, and a cam with a special profile was used as a clicking mechanism for quick release of elastic energy stored in the springs to create a sudden kick for a quick jump. Performance analysis and experiments were conducted for comparison and performance estimation of the jumping mechanism prototype. Our prototype could produce standing jumps over obstacles that were about 14 times its own size （approximate to 71 cm） and a jumping distance of 20 times its own size （approximate to 100 cm）.展开更多
The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end...The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end-effectors have some disadvantages,such as poor misalignment tolerance capability and complex mechanical components.According to the end positioning errors and the residual vibration characters of the large space manipulators,two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed.And the end-effector should accommodate the following misalignments of the mechanical interface.The translation misalignments in axial and radial directions and the angular misalignments in roll,pitch and yaw are ±100 mm,100 mm,±10°,±15°,±15°,respectively.Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily.The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes,and they are designed in detail.The capabilities of misalignment tolerance and soft capture are validated and evaluated,through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software.The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement.And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll,pitch and yaw of the steel cable-snared end-effector are 30mm,15mm,6°,3° and 3° larger than those of the three fingers-three petals end-effector,respectively.And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector.The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.展开更多
Severe earthquakes continue to cause major catastrophes. Many devices in active, hybrid, and semi-active structural control systems which are used as controllable force devices are costly to build and maintain. The pa...Severe earthquakes continue to cause major catastrophes. Many devices in active, hybrid, and semi-active structural control systems which are used as controllable force devices are costly to build and maintain. The passive control reinforced concrete frame （PCRCF） reinforced with high strength steel only in the columns presented here provides structural systems more resistance to lateral earthquake loadings at comparatively lower cost. The effectiveness is demonstrated by a nonlinear static analysis using fiber model for a single story single bay frame. The study shows that the use of high performance steel in columns prevents formation of plastic hinges at the critical column base sections and failures are always initiated by reinforcement yielding at the beam ends. Furthermore, after experiencing severe lateral drift, the passive control design has small residual displacements compared to ordinary reinforced concrete frames. PCRCF rehabilitation and strengthening can be achieved more easily as compared with ordinary reinforced concrete frame.展开更多
This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas ...This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas diffusion in boundary layer and the equilibrium relations in surface chemical reactions. Simultaneously, an engineering equation to predict the oxygen partial pressure of active-to-passive transition was derived under the specific temperature zone. The results indicated that the active-to-passive oxidation transition of C/SiC is closely related to the composition of the material. At certain temperature and oxygen partial pressure conditions, the composite with high carbon content is prone to cause active oxidation which is negative to the oxidation resistance of the material.展开更多
由于电网阻抗的耦合作用,基于LCL滤波器并网的光伏逆变器会产生谐振。为了抑制逆变器并网时产生的谐振,文章首先分析了滤波电容串联电阻的无源阻尼的控制,并在此基础上推导出等效的有源阻尼的控制方法,同时对比了无源阻尼和有源阻尼的特...由于电网阻抗的耦合作用,基于LCL滤波器并网的光伏逆变器会产生谐振。为了抑制逆变器并网时产生的谐振,文章首先分析了滤波电容串联电阻的无源阻尼的控制,并在此基础上推导出等效的有源阻尼的控制方法,同时对比了无源阻尼和有源阻尼的特点,分析了阻尼系数、虚拟电阻和电容电流反馈系数之间的关系。建立了包含有源阻尼的逆变器并网闭环数学模型,在此模型基础上,分析了阻尼系数对控制系统性能的影响。最后在10 k W并网逆变器上进行了实验,实验结果表明,文章采用的有源阻尼控制策略能够有效地抑制并网谐振。展开更多
To explore hostile extraterrestrial landforms and construct an engineering prototype,this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander(ReLML)with three operation mo...To explore hostile extraterrestrial landforms and construct an engineering prototype,this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander(ReLML)with three operation modes from adjusting,landing,to roving.Compared with our preceding works,the adjusting mode with three rotations(3R)provides a totally novel exploration approach to geometrically matching and securely arriving at complex terrains dangerous to visit currently;the landing mode is redefined by two rotations one translation(2R1T),identical with the tried-and-tested Apollo and Chang'E landers to enhance survivability via reasonable touchdown buffering motion;roving mode also utilizes 2R1T motion for good motion and force properties.The reconfigurable mechanism theory is first brought into synthesizing legged mobile lander integrating active and passive metamorphoses,composed of two types of metamorphic joints and metamorphic execution and transmission mechanisms.To reveal metamorphic principles with multiple finite motions,the finite screw theory is developed to present the procedure from unified mathematical representation,modes and source phase derivations,metamorphic joint and limb design,to final structure assembly.To identify the prototype topology,the 3D optimal selection matrix method is proposed considering three operation modes,five evaluation criteria,and two topological subsystems.Finally,simulation verifies the whole task implementation process to ensure the reasonability of design.展开更多
文摘A jumping mechanism can be an efficient mode of motion for small robots to overcome large obstacles on the ground and rough terrain. In this paper, we present a 7 g prototype of locust-inspired jumping mechanism that uses springs, wire, reduction gears, and a motor as the actuation components. The leg structure and muscles of a locust or grasshopper were mimicked using springs and wire, springs for passive extensor muscles, and a wire as a flexor muscle. A small motor was used to slowly charge the spring through a lever and gear system, and a cam with a special profile was used as a clicking mechanism for quick release of elastic energy stored in the springs to create a sudden kick for a quick jump. Performance analysis and experiments were conducted for comparison and performance estimation of the jumping mechanism prototype. Our prototype could produce standing jumps over obstacles that were about 14 times its own size （approximate to 71 cm） and a jumping distance of 20 times its own size （approximate to 100 cm）.
基金supported by National Hi-tech Research and Development Program of China(863 Program,Grant No. 2006AA04Z228)
文摘The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end-effectors have some disadvantages,such as poor misalignment tolerance capability and complex mechanical components.According to the end positioning errors and the residual vibration characters of the large space manipulators,two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed.And the end-effector should accommodate the following misalignments of the mechanical interface.The translation misalignments in axial and radial directions and the angular misalignments in roll,pitch and yaw are ±100 mm,100 mm,±10°,±15°,±15°,respectively.Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily.The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes,and they are designed in detail.The capabilities of misalignment tolerance and soft capture are validated and evaluated,through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software.The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement.And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll,pitch and yaw of the steel cable-snared end-effector are 30mm,15mm,6°,3° and 3° larger than those of the three fingers-three petals end-effector,respectively.And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector.The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.
基金Supported by the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20040003095) and the Cul-tivation Fund of the Key Grant Scientific and Technical Innova-tion Project, Ministry of Education of China (No. 704003)
文摘Severe earthquakes continue to cause major catastrophes. Many devices in active, hybrid, and semi-active structural control systems which are used as controllable force devices are costly to build and maintain. The passive control reinforced concrete frame （PCRCF） reinforced with high strength steel only in the columns presented here provides structural systems more resistance to lateral earthquake loadings at comparatively lower cost. The effectiveness is demonstrated by a nonlinear static analysis using fiber model for a single story single bay frame. The study shows that the use of high performance steel in columns prevents formation of plastic hinges at the critical column base sections and failures are always initiated by reinforcement yielding at the beam ends. Furthermore, after experiencing severe lateral drift, the passive control design has small residual displacements compared to ordinary reinforced concrete frames. PCRCF rehabilitation and strengthening can be achieved more easily as compared with ordinary reinforced concrete frame.
基金supported by the National Natural Science Foundation of China (Grant No. 11172284)the International Science and Technology Cooperative Project from Ministry of Science and Technology (GrantNo. 2013DFA30820)
文摘This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas diffusion in boundary layer and the equilibrium relations in surface chemical reactions. Simultaneously, an engineering equation to predict the oxygen partial pressure of active-to-passive transition was derived under the specific temperature zone. The results indicated that the active-to-passive oxidation transition of C/SiC is closely related to the composition of the material. At certain temperature and oxygen partial pressure conditions, the composite with high carbon content is prone to cause active oxidation which is negative to the oxidation resistance of the material.
文摘由于电网阻抗的耦合作用,基于LCL滤波器并网的光伏逆变器会产生谐振。为了抑制逆变器并网时产生的谐振,文章首先分析了滤波电容串联电阻的无源阻尼的控制,并在此基础上推导出等效的有源阻尼的控制方法,同时对比了无源阻尼和有源阻尼的特点,分析了阻尼系数、虚拟电阻和电容电流反馈系数之间的关系。建立了包含有源阻尼的逆变器并网闭环数学模型,在此模型基础上,分析了阻尼系数对控制系统性能的影响。最后在10 k W并网逆变器上进行了实验,实验结果表明,文章采用的有源阻尼控制策略能够有效地抑制并网谐振。
基金Supported by National Natural Science Foundation of China(Grant No.51735009)State Key Lab of Mechanical System and Vibration Project of China(Grant No.MSVZD202008)National Aerospace Science Foundation of China(040102).
文摘To explore hostile extraterrestrial landforms and construct an engineering prototype,this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander(ReLML)with three operation modes from adjusting,landing,to roving.Compared with our preceding works,the adjusting mode with three rotations(3R)provides a totally novel exploration approach to geometrically matching and securely arriving at complex terrains dangerous to visit currently;the landing mode is redefined by two rotations one translation(2R1T),identical with the tried-and-tested Apollo and Chang'E landers to enhance survivability via reasonable touchdown buffering motion;roving mode also utilizes 2R1T motion for good motion and force properties.The reconfigurable mechanism theory is first brought into synthesizing legged mobile lander integrating active and passive metamorphoses,composed of two types of metamorphic joints and metamorphic execution and transmission mechanisms.To reveal metamorphic principles with multiple finite motions,the finite screw theory is developed to present the procedure from unified mathematical representation,modes and source phase derivations,metamorphic joint and limb design,to final structure assembly.To identify the prototype topology,the 3D optimal selection matrix method is proposed considering three operation modes,five evaluation criteria,and two topological subsystems.Finally,simulation verifies the whole task implementation process to ensure the reasonability of design.
