Research on valve core’s clamping stagnation of double flapper-nozzle servo valve

Due to great changing of instantaneous temperature of hydraulic oil of double flapper-nozzle servo valve, thermal deformation between valve core and valve sleeve may result in catching phenomenon of valve core, and then the reliability of servo valve could be affected seriously. The work focuses on a particular model of double flapper-nozzle servo valve and establishes three dimension couple models of liquid-solid-thermal under extreme operating condition. The transmission route and dissipative mechanism of heat is revealed and thermal deformation behavior of valve core and valve sleeve is researched. A change law of the key fit clearance under the effect of thermal expansion and warp deformation is explored, the source of catching phenomenon of valve core is identified, and then preventive measure and improvement can be proposed. In order to verify the correctness of theoretical analysis, the moving smoothness of deformed valve core and reground valve core under the circumstance of high-temperature hydraulic oil on electrohydraulic servo valve static characteristics test table is compared and tested. The results show that as oil temperature rises, relative deformations between valve core and valve sleeve in different direction at a same cross-section are not equal, and then the key fit clearance is less than the initial value. Relative deformations in the same direction at different axial position are not equal, the deformations of middle and two ends are maximum and minimum values respectively, and then warp deformation of valve core occurs. When oil temperature is higher, the relative deformations between valve core and valve sleeve is larger, the moving smoothness of valve core gets worse, and the catching phenomenon of valve core occurs. Axial deformation of valve sleeve and valve core at different axial position is different, and the opening coefficient and stability of servo valve could be affected, especially the operation circumstance of small opening. The study can provide some guidance for designing double nozzle flapper servo valves.

Form Properties of Moving Targets Bias Smooth Pursuit Target Selection in Monkeys

During natural viewing,we often recognize multiple objects,detect their motion,and select one object as the target to track.It remains to be determined how such behavior is guided by the integration of visual form and motion perception.To address this,we studied how monkeys made a choice to track moving targets with different forms by smooth pursuit eye movements in a two-target task.We found that pursuit responses were biased toward the motion direction of a target with a hole.By computing the relative weighting,we found that the target with a hole exhibited a larger weight for vector computation.The global hole feature dominated other form properties.This dominance failed to account for changes in pursuit responses to a target with different forms moving singly.These findings suggest that the integration of visual form and motion perception can reshape the competition in sensorimotor networks to guide behavioral selection.