Feasibility Study On Problems Related To Aligning The Sensitive Axis Of A Superconducting Gravity Gradiometer

The accurate measurement of gravity acceleration or gravity field distribution has important strategic significance and practical application value in geological survey and research,exploration of oil and gas deposits and marine resources,high-precision inertial guidance and research on atmospheric,space solar radiation pressure,earth diffuse reflection,etc.Using the magnetically levitated superconducting test mass instead of the traditional spring oscillator,a superconducting gravity gradiometer composed of two separate superconducting accelerometers coupled together through a superconducting circuit is being developed at our laboratory.Since the gravity gradient is measured based on the differential-modes displacement,the orientation of the sensitive axes of the two accelerometers,as well as the angle between their baseline direction and average sensitive direction,are key factors affecting the accuracy of the measurement value.In this paper,the feasibility of piezoelectric motor driven accelerometer movement for sensitive axis alignment and the performance of thermal insulation materials used to isolate piezoelectric motor and accelerometer are analyzed and experimentally studied.The main work of this thesis is summarized as followsFirstly,for the superconducting gravity gradiometer composed of two separate superconducting accelerometers,the source of geometric error of the superconducting gravity gradiometer is analyzed theoretically,and it is pointed out that adjusting the sensitive axis orientation of the two accelerometers is the key to improve the measurement accuracy of the gravity acceleration.Furthermore,based on the characteristics of piezoelectric motor driving the movement of the load,the adjustment scheme of sensitive axis orientation of two accelerometers in superconducting gravity gradiometer is analyzed and discussedSecond,in order to verify the feasibility of the accelerometer driven by displacement actuator based on piezoelectric motor,as one of the main participants,we developed two sets of testing systems for room temperature driving and low temperature driving respectively.Based on the room temperature testing system,the running stability of the displacement actuator based on piezoelectric motor and the relationship between the frequency and step size and the moving speed of the displacement actuator are experimentally studied.The results show that the displacement actuator can work stably in the order of 1 μ m,and the good and stable operation of the displacement actuator can be achieved by changing the frequency or step size.For the low temperature drive mobile testing system,only the drawing design and component processing have been completed.The assembly and debugging of the low temperature drive mobile test system could not be completed on time.Third,because piezoelectric motor is a kind of displacement actuator which converts electrical pulse into mechanical motion,the heat generated during the execution is transferred to the accelerometer which would affect the performance of the accelerometer.Therefore,thermal insulation materials are used to isolate the piezoelectric motor from the rigid frame where the accelerometer is placed.The heat transfer performance of the heat insulation material was evaluated by thermal conductivity measurement.Considering comprehensively,epoxy resin can be used as a bonding and thermal insulation material for different parts in a superconducting gravity gradiometer.