Effect of time-varying factors on the drift model of Electrostatically Supported Gyro
Time-varying factors are extremely important in both dual-axis servo turntable and Electrostatically Supported Gyro (ESG) by affecting the testing of ESG's drift model. In this paper, we model four time-varying factors, gyro case mis-alignment angle, installation error between gyro and inner ring platform, turntable base fluctuation, and null position drift of turntable's angle sensor, as a polynomial of time in the drift model for pole ESG. Based on the kinematic formula of turntable in pole gyro mode, we derive the relationships between the time-varying factors and angles of inner and outer rings of the turntable. Then the cases that these four time-varying factors affect the trajectory of turntable are analyzed term-by-term. We find that the constant drift, gravity-related drift and random drift are greatly affected by these four factors. In the light of these analyses, several basic principles to control these factors are further proposed.
Selection of electrodes geometry for contactless suspension of a conducting sphere
Electrostatically supported gyroscope (ESG) is the key component of long-term autonomous navigation system by virtue of its high precision. With the aid of the case rotation-dwell technology, the case-fixed drift of the ESG is largely averaged out and then the precision is mainly determined by the rotor roundness, electrodes geometry, suspension control law and circumstances stability. With the certain manufacturing limit and careful suspension system design, the factors of rotor roundness, circumstances stability and suspension fluctuation are already bounded to a certain level, so it is important to check the electrodes geometry to improve the performance of the ESG. In this paper, aiming to minimize the drift of gyroscope, the problem of determining the electrodes geometry is addressed with compromising suspension stiffness and practical realization. Firstly, a general drift model is put forward for arbitrary electrodes geometry and rotor attitude. It is found that the drift along the electrode axis vanishes when the rotor rotation axis coincides with this very electrode axis and the drift model turns to be simpler. Then, the effect of electrode shape on disturbing torque is analyzed with identical electrodes and isotropic stiffness. It is found that when the electrode shape is symmetrical about its geometry axis, the drift caused by cross-axis effect will be minimized and a simplest drift model can be potentially obtained with some sacrifices on suspension stiffness. Finally, two commonly used electrodes shape, hexahedral projection electrodes and spherical crown electrodes which respectively represents the potential maximal stiffness and the simplest form are compared with its drift magnitude, model cleanliness, suspension stiffness, disturbing torque, cross-axis effect and engineering realization. The result is useful in problem of electrode geometry selection.
Heat Transfer Characteristic for a New Plate Metal Hydride Reactor
The property of major metal hydride reactors in the world was analyzed and a new plate metal hydride reactor was designed.An experimental facility to test the metal hydride reactor was also designed correspondingly.The effective thermal conductivity of the plate metal hydride reactor was measured by varying the initial metal hydride packing fraction,the kind of filled gas and the pressure of the filled gas,cycle numbers.The test results show that the effective thermal conductivity of the reactor,has exceeded(7.5) W/(m·K) before activation,which is increased greatly.After alloy activation,the effective thermal conductivity of the reactor has a linear change trend with the hydrogen pressure during the interval 0.1~3.5 MPa.The effective thermal conductivity of the reactor just only decreases quickly at the beginning,but becomes stable after several cycles.