Cross-spring pivots, formed by crossing two identical flexural beams at their midpoint, have been broadly used in precision engineering and aerospace fields. Many researches have been conducted on modeling and analysi...Cross-spring pivots, formed by crossing two identical flexural beams at their midpoint, have been broadly used in precision engineering and aerospace fields. Many researches have been conducted on modeling and analysis of cross-spring pivots. However the influence of application position and magnitude of the external loads on the load-rotation and parasitic motion characteristics has not yet been discussed. In order to reveal the effect of the external loads, this paper develops the accurate load-rotation and center shift models of cross-spring pivots, with generalized planar loads applied including bending moment, horizontal and vertical forces. Firstly, by using the energy method, the load-displacement models of the pivot are derived with the assumption of small rotational angles. Based on the models, the influence of generalized planar loads on the load-rotation relationship is discussed, which shows that both application position and magnitude of the vertical and horizontal forces influence the load-rotation behaviors. Then the accurate center shift expressions of the pivot with generalized planar loads are developed, which shows that the rotational angle is the dominant term for both components of the center shift while the vertical and horizontal forces are small. Finally, the accuracy of the proposed model is validated by finite element analysis（FEA）. Comparing the model data with the results obtained from FEA, the relative error of the load-rotation is less than 6% even if the rotational angle reaches 20°; the relative errors of the two components of center shift are less than 5% and 10% respectively when the rotational angle reaches 10°. The proposed model and analytical conclusions can be used to analyze and preliminarily design the compliant mechanisms containing cross-spring pivots.展开更多
This paper presents an electromagnetic three-dimensional vibration energy harvesting device that uses an oblique cross-spring vibrator structure to collect low-frequency vibration energy.The oblique cross-spring struc...This paper presents an electromagnetic three-dimensional vibration energy harvesting device that uses an oblique cross-spring vibrator structure to collect low-frequency vibration energy.The oblique cross-spring structure allowed the center vibrator to vibrate in any direction.Together with six-directional coils,this configuration senses and harvests environmental vibrations across all directions and levels.First,the dynamics of the oblique cross-spring vibrator structure were analyzed and a finite element simulation was performed for the magnet arrangement and mode shape of the structure.A prototype is designed,fabricated,and experimentally verified.The results showed that the efficiency of the three-dimensional energy output was higher under the same excitation,which was 2.7 times higher than that of the unidirectional output.The unidirectional output power with load is 0.94 mW at 11 Hz under 0.3 g base excitation.The highest total output power of the prototype was 50 mW when it was fixed to the leg at a running speed of 8 km/h.Consequently,the energy harvesting scheme proposed in this study has a considerable low-frequency output effect,which provides a novel means of improving the electrical performance of energy harvesting systems for self-powered IoT and sensor devices.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos. 50975007, 51105014)PhD Programs Foundation of Ministry of Education of China(Grant No. 20091102110023)China Postdoctoral Science Foundation(Grant No. 20100480179)
文摘Cross-spring pivots, formed by crossing two identical flexural beams at their midpoint, have been broadly used in precision engineering and aerospace fields. Many researches have been conducted on modeling and analysis of cross-spring pivots. However the influence of application position and magnitude of the external loads on the load-rotation and parasitic motion characteristics has not yet been discussed. In order to reveal the effect of the external loads, this paper develops the accurate load-rotation and center shift models of cross-spring pivots, with generalized planar loads applied including bending moment, horizontal and vertical forces. Firstly, by using the energy method, the load-displacement models of the pivot are derived with the assumption of small rotational angles. Based on the models, the influence of generalized planar loads on the load-rotation relationship is discussed, which shows that both application position and magnitude of the vertical and horizontal forces influence the load-rotation behaviors. Then the accurate center shift expressions of the pivot with generalized planar loads are developed, which shows that the rotational angle is the dominant term for both components of the center shift while the vertical and horizontal forces are small. Finally, the accuracy of the proposed model is validated by finite element analysis（FEA）. Comparing the model data with the results obtained from FEA, the relative error of the load-rotation is less than 6% even if the rotational angle reaches 20°; the relative errors of the two components of center shift are less than 5% and 10% respectively when the rotational angle reaches 10°. The proposed model and analytical conclusions can be used to analyze and preliminarily design the compliant mechanisms containing cross-spring pivots.
基金supported by the National Natural Science Foundation of China(Grant Nos.62188101,12132002,12302010)。
文摘This paper presents an electromagnetic three-dimensional vibration energy harvesting device that uses an oblique cross-spring vibrator structure to collect low-frequency vibration energy.The oblique cross-spring structure allowed the center vibrator to vibrate in any direction.Together with six-directional coils,this configuration senses and harvests environmental vibrations across all directions and levels.First,the dynamics of the oblique cross-spring vibrator structure were analyzed and a finite element simulation was performed for the magnet arrangement and mode shape of the structure.A prototype is designed,fabricated,and experimentally verified.The results showed that the efficiency of the three-dimensional energy output was higher under the same excitation,which was 2.7 times higher than that of the unidirectional output.The unidirectional output power with load is 0.94 mW at 11 Hz under 0.3 g base excitation.The highest total output power of the prototype was 50 mW when it was fixed to the leg at a running speed of 8 km/h.Consequently,the energy harvesting scheme proposed in this study has a considerable low-frequency output effect,which provides a novel means of improving the electrical performance of energy harvesting systems for self-powered IoT and sensor devices.
