Variable-Structure Feedback Control for Non-sensitive Degrees of Freedom in Superconducting Gravity Gradiometers

The airborne superconducting gravity gradiometer is currently a cutting-edge topic in the field of gravity exploration instrument development. In airborne environments, the resolution of superconducting gravity gradiometers is limited by cross-coupling noise, making further improvement challenging. To suppress the cross-coupling noise in superconducting gravity gradiometers, it is necessary to implement feedback control on the motion of test masses in non-sensitive degrees of freedom. To address this issue, this paper proposes a variable-structure feedback control method for non-sensitive degrees of freedom. By establishing an equivalent spring oscillator model and piecewise phase trajectory equations, a variable-structure feedback controller based on analogue circuits is designed and implemented. Experimental results validate the feasibility and effectiveness of the proposed method. Under laboratory conditions, displacement residuals are reduced by approximately 50%, and the power spectral density in the 10–20 Hz frequency band is lowered by about one order of magnitude.