HIGH-PRECISION MAGNETIC SUSPENSION ACCELEROMETER

• US 20170242050A1
• Filed: 02/17/2017
• Published: 08/24/2017
• Est. Priority Date: 02/18/2016
• Status: Active Grant

• Current Assignee: China Three Gorges University
• Original Assignee: China Three Gorges University
• Inventors: PAN, Liqing, YANG, Xianwei, LUO, Zhihui, ZHAO, Hua, SHAO, Mingxue, REN, Qiongying, TAN, Chao, LIU, Min, WANG, Chao, ZHANG, Chao, ZHENG, Sheng, PIAO, Hongguang, LU, Guangduo, XU, Yunli, HUANG, Xiufeng
• Granted Patent: US 10,444,257 B2
• Time in Patent Office: Days
• CPC Class Codes: B64G 1/22 Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
• CPC Class Codes: B64G 1/36 using sensors, e.g. sun-sensors, horizon sensors
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01P 15/132 with electromagnetic counterbalancing means
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A high-precision magnetic suspension accelerometer for measuring the linear acceleration of a spacecraft is provided, comprising a magnetically shielded vacuum chamber system, a magnetic displacement sensing system, a magnetic suspension control system and a small magnetic proof mass. A optical coherence displacement detection technique is utilized for precisely measuring the position and the posture of the small magnetic proof mass in real time, and a magnetic suspension control technique is utilized for precisely controlling the position and the posture of the small magnetic proof mass to be brought back to the origin, so as to keep the small magnetic proof mass in the center of the systemic inner chamber. When the spacecraft is subject to a non-conservative force, the magnitude and direction of the acceleration can be precisely measured via the measurement of currents in the position control coils due to the acceleration of the spacecraft proportional to the currents of the position control coils. The accelerometer of the invention can avoid the technical bottleneck of high-precision machining, is easy to be produced and can achieve more high-precision measurement of the acceleration vector.

Claims

1. A high-precision magnetic suspension accelerometer, comprising a magnetically shielded vacuum chamber system, an optical coherence displacement detecting system, a magnetic suspension control system and a small magnetic proof mass,

wherein, the magnetically shielded vacuum chamber system comprises a magnetically shielded outer chamber and a systemic inner chamber which is disposed inside the magnetically shielded outer chamber and vacuum, with the small magnetic proof mass disposed inside the systemic inner chamber;

the optical coherence displacement detecting system, disposed on the systemic inner chamber, is used for monitoring the position and the posture of the small magnetic proof mass in real time by sending an optical signal to the small magnetic proof mass and receiving an optical signal reflected back;

the magnetic suspension control system, disposed on the systemic inner chamber, is used for controlling the position and the posture of the small magnetic proof mass in real time to keep it levitating in the center of the systemic inner chamber constantly; and

the center of the systemic inner chamber is coincident with the center of mass of a spacecraft.

2. The accelerometer of claim 1, wherein the optical coherence displacement detecting system comprises a plurality of pairs of interferometer probes with each pair connected to an optical displacement detecting device via an optical fiber,

wherein, the optical displacement detecting device is a Michelson or Fabry-Perot displacement detecting device and the interferometer probes are located at different positions inside the systemic inner chamber;

a light source sends optical signals to the small magnetic proof mass via each pair of the interferometer probes in the system and receives optical signals reflected back by it, the optical signals containing the information of the position and the posture of the small magnetic proof mass;

the optical signals are transmitted to the optical displacement detecting device through the optical fiber, and processed according to the principle of optical interference to transfer the displacements and the deflection angles of the small magnetic proof mass into the change of the interfered light; and

based on measurement results of each pair of the interferometer probes and by a calculation according to the principle of vector addition, the displacement of the small magnetic proof mass deviating from the center of the systemic inner chamber, and the rotation angle of it rotating about two rotational axes perpendicular to the direction of the magnetic moment, are be finally determined according to the change in displacement of each probe point and fed back to the magnetic suspension control system to control the position and the posture of the small magnetic proof mass in real time.

3. The accelerometer of claim 2, wherein five pairs of the interferometer probes are provided,

wherein three pairs of these are provided in the x-direction of the systemic inner chamber, i.e., on the left and right chamber walls,

wherein one pair of the three pairs, arranged on the right chamber wall along the y-direction and vertically symmetrical about the face center, is used for measuring the posture change of the small magnetic proof mass rotating about the z-axis;

another pair of the three ones, arranged on the right chamber wall along the z-direction and horizontally symmetrical about the face center, is used for measuring the posture change of the small magnetic proof mass rotating about the y-axis; and

the last pair of the three ones, arranged in centers of the left and right chamber walls along the x-direction, is used for measuring the translational displacement of the small magnetic proof mass in the x-direction;

one pair of the five ones, provided in the y-direction of the systemic inner chamber, i.e., in centers of the upper and lower chamber walls, is used for measuring the translational displacement of the small magnetic proof mass in the y-direction; and

the last pair of the five ones, provided in the z-direction of the systemic inner chamber, i.e., in centers of the front and rear chamber walls, is used for measuring the translational displacement of the small magnetic proof mass in the z-direction.

4. The accelerometer of claim 1, wherein the magnetic suspension control system comprises a plurality of pairs of position control coils arranged symmetrically on the left and right side walls of the systemic inner chamber and a plurality of posture control coils arranged symmetrically on the upper, lower, front and rear side walls of the systemic inner chamber,

wherein the magnetic suspension control system receives a feedback from the magnetic displacement sensing system via the position control coils and the posture control coils, and controls the position and the posture of the small magnetic proof mass in real time to keep it levitating in the center of the systemic inner chamber constantly, and

the center of the systemic inner chamber is coincident with the center of mass of the spacecraft.

5. The accelerometer of claim 4, wherein four pairs of the position control coils, symmetric about the x-axis, are mounted on the left and right chamber walls in the x-direction of the systemic inner chamber, and are capable of making the center of mass of the small magnetic proof mass kept in the center of the systemic inner chamber constantly by being applied with currents in different directions and with different intensities.

6. The accelerometer of claim 4, wherein two pairs of the posture control coils are mounted in centers of the upper and lower chamber walls of the systemic inner chamber in the y-direction and in centers of the front and rear chamber walls in the z-direction respectively,

wherein the diameter of the posture control coils is considerably greater than the overall dimension of the small magnetic proof mass, and the posture control coils are used for controlling the posture of the small magnetic proof mass to keep the equivalent magnetic moment of the small magnetic proof mass in the x-direction constantly.

7. The accelerometer of claim 4, wherein in the control of the translational motion and the rotation of the small magnetic proof mass, the electromagnetic force, acting on the small magnetic proof mass and generated by the position control coils, counteracts the acceleration generated by the spacecraft subject to an non-conservative force, keeping the center of mass of the small magnetic proof mass constantly coincident with the center of mass of the spacecraft,

wherein, a relationship between the magnetic force vector F and the acceleration vector a is expressed by F=ma where m denotes the mass of the small magnetic proof mass, the magnitude of the electromagnetic force is proportional to the magnitude of the magnetic field generated by the position control coils, the magnitude of the magnetic field generated by the position control coils is proportional to the magnitude of the current, and the acceleration of the spacecraft can be measured precisely via the current applied in the position control coils.

8. The accelerometer of claim 1, wherein the small magnetic proof mass is cylindrical.

9. The accelerometer of claim 1, wherein the small magnetic proof mass is made of permanent magnetic material, or an inner core of a permanent magnet is used as the small magnetic proof with outside of the inner core covered with non-magnetic material.

10. A high-precision magnetic suspension accelerometer, for measuring the linear acceleration of a spacecraft, comprising a magnetically shielded vacuum chamber system, a magnetic displacement sensing system, a magnetic suspension control system and a small magnetic proof mass,

wherein, the magnetically shielded vacuum chamber system comprises a magnetically shielded outer chamber and a systemic inner chamber which is disposed inside the magnetically shielded outer chamber and vacuum;

the magnetic displacement sensing system comprises a plurality of high-precision magnetic sensors disposed at different positions inside the systemic inner chamber for monitoring the position and the posture of the small magnetic proof mass in real time through the detection of magnetic signals of the proof mass;

the magnetic suspension control system comprises a plurality of groups of position control coils arranged symmetrically on the left and right side walls of the systemic inner chamber and a plurality of groups of posture control coils arranged symmetrically on the upper, lower, front and rear side walls of the systemic inner chamber;

the magnetic suspension control system receives a feedback from the magnetic displacement sensing system via the position control coils and the posture control coils, and controls the position and the posture of the small magnetic proof mass in real time to keep it levitating in the center of the systemic inner chamber constantly; and

the center of the systemic inner chamber is coincident with the center of mass of a spacecraft.

11. The accelerometer of claim 10, wherein in the control of the translational motion and the rotation of the small magnetic proof mass, the electromagnetic force, acting on the small magnetic proof mass and generated by the position control coils, counteracts the acceleration generated by the spacecraft subject to a non-conservative force, keeping the center of mass of the small magnetic proof mass constantly coincident with the center of mass of the spacecraft,

wherein, a relationship between the magnetic force vector F and the acceleration vector a is expressed by F=ma where m denotes the mass of the small magnetic proof mass, the magnitude of the electromagnetic force is proportional to the magnitude of the magnetic field generated by the position control coils, the magnitude of the magnetic field generated by the position control coils is proportional to the magnitude of the current, and the acceleration of the spacecraft can be measured precisely via the current applied in the position control coils.

12. The accelerometer of claim 10, wherein the magnitude of the magnetic fields measured by the magnetic sensors is related to the position and the posture of the small magnetic proof mass;

the each corresponding coordinate system of the magnetic sensors is assumed to be a space global coordinate system, the coordinates of the center of mass of the small magnetic proof mass are denoted as (x₀, y₀, z₀), the coordinates of the probe point P as (x, y, z) and the distance between the center of mass of the small magnetic proof mass and the probe point as r;

when this distance between the center of mass of the small magnetic proof mass and the probe point is considerably larger than the size of the small magnetic proof mass, the small magnetic proof mass can be approximated as a magnetic dipole;

the equivalent magnetic moment vector of the small magnetic proof mass is denoted as {right arrow over (M)}, an azimuthal angle and an elevation angle of {right arrow over (M)} in the space coordinate system are denoted as α and

β

respectively;

according to equations for components of the magnetic field of the probe point, i.e.,

13. The accelerometer of claim 10, wherein the magnetic suspension control system comprises four groups of position control coils and two groups of posture control coils,

wherein, the center of mass of the small magnetic proof mass can be kept in the center of the systemic chamber constantly by applying currents in different directions and with different intensities in the four groups of the position control coils;

and

the two groups of the posture control coils are used for controlling the posture of the small magnetic proof mass and keeping the magnetic moment of the small magnetic proof mass in the x-direction constantly.

14. The accelerometer of claim 10, wherein the small magnetic proof mass is spheroidal, circular or cylindrical.

15. The accelerometer of claim 10, wherein the small magnetic proof is made of permanent magnetic material, or an inner core of a permanent magnet is used as the small magnetic proof with outside of the inner core covered with non-magnetic material.