Absolute gravimeter falling body and trailer separation distance measurement system and measurement method

Abstract

The present invention discloses a system and method for measuring the separation distance between a falling object and a trailer of an absolute gravimeter, comprising an absolute gravimeter vacuum chamber, a falling object and a trailer cover in the absolute gravimeter vacuum chamber, and upper and lower interferometers, wherein the upper interferometer and the lower interferometer are respectively arranged at the top and the bottom of the absolute gravimeter vacuum chamber, the falling object is arranged inside the trailer cover, the trailer cover comprises a metal shell and a trailer cover corner cone prism, the trailer cover corner cone prism is located inside the metal shell and fixed to the metal shell with the bottom facing upward, and the trailer cover is fixed on the trailer and moves with the trailer. The present invention is reasonably designed and can realize non-contact measurement of the separation distance between a falling object and a trailer without almost changing the original mechanical structure of the absolute gravimeter, and has the effects of simple installation, convenient operation, and wide applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of gravity precision measurement, and in particular to a system and method for measuring the separation distance between a falling object and a trailer of an absolute gravimeter. Background Art

[0002] Gravitational acceleration is a geophysical parameter that changes with time and space. It has important applications in geodesy, precision measurement, assisted navigation, military defense, etc. At present, the optical interferometer absolute gravimeter is one of the main instruments for measuring gravitational acceleration. Its measurement principle is to measure the displacement and time of the falling body along the direction of gravity during the falling process by measuring the displacement and time of the falling body along the direction of gravity, and use polynomial fitting to obtain the gravitational acceleration value.

[0003] Optical interferometric absolute gravimeter (hereinafter referred to as absolute gravimeter) usually uses a motor to drive a tractor to move downward along a guide rod. When the tractor's acceleration is greater than the gravity acceleration g, the falling body separates from the tractor, thereby ensuring the free fall of the falling body. This is a falling body motion control system that is currently widely used. Ideally, the falling body will move according to the motion design curve, the tractor and the falling body will quickly separate and maintain the set separation distance unchanged, and the falling body will fall freely; when the free fall ends, the separation distance between the tractor and the falling body gradually decreases and the instantaneous speed of the two is the same at the moment of contact, that is, "soft landing", and finally decelerate to a standstill together. However, during the actual installation and adjustment of the absolute gravimeter, due to the limitations of the machining accuracy of the guide rod and the installation and adjustment accuracy of the tractor device, the loads of different sets of instruments are different, which leads to large differences in the falling motion of the falling body in different sets of absolute gravimeters for the same falling body motion design curve. In order to improve the accuracy and repeatability of the falling motion of different sets of absolute gravimeters, it is necessary to measure the separation distance between the falling object and the trailer during the falling process, and use the measurement results to optimize the falling motion.

[0004] At present, the technology used in the FG5 absolute gravimeter produced by Microg Company in the United States is to install an LED light source and a one-dimensional position detector on the trailer, and install a glass ball on the falling object. The light emitted by the LED is refracted by the glass ball and converges on the one-dimensional position detector. When the falling object begins to separate from the trailer, the glass ball moves upward relative to the trailer, and the position of the light hitting the one-dimensional position detector after being refracted by the glass ball will change. The one-dimensional position detector converts the received light signal into a displacement signal, which is the separation distance between the falling object and the trailer during the fall. In addition, no other literature has been found to study this issue.

[0005] The existing technology requires the installation of LED light sources, one-dimensional position detectors and supporting wires on a trailer with narrow space. The installation of a glass ball on the falling object also requires the change of the structure of the falling object. In addition, all the above devices must work in a high vacuum environment, which has high requirements for the degassing rate of the devices. This technology has a complex structure, is difficult to install and maintain, and has certain limitations when used. Therefore, we designed an absolute gravimeter falling object and trailer separation distance measurement system and measurement method to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art, and to propose an absolute gravimeter falling body and trailer separation distance measurement system and measurement method, which can realize non-contact measurement of the separation distance between the falling body and the trailer without almost changing the original absolute gravimeter mechanical structure, and has the effects of simple installation, convenient operation and wide applicability.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A system and method for measuring the separation distance between a falling object and a trailer of an absolute gravimeter, comprising a vacuum chamber of the absolute gravimeter, a falling object and a trailer cover in the vacuum chamber of the absolute gravimeter, and an upper and lower set of interferometers, wherein the upper interferometer and the lower interferometer are respectively arranged at the top and the bottom of the vacuum chamber of the absolute gravimeter, and the falling object is arranged inside the trailer cover.

[0009] Preferably, the trailer cover comprises a metal shell and a trailer cover corner cube prism, the trailer cover corner cube prism is located in the metal shell and fixed to the metal shell with the bottom facing upward, and the trailer cover is fixed on the trailer and moves with the trailer.

[0010] Preferably, the main component of the falling object is a falling corner pyramid prism with the bottom facing downward, and the falling object is placed on a trailer. When the trailer accelerates and moves downward, the falling object separates from the trailer.

[0011] Preferably, the upper interferometer comprises an upper laser light source, an upper beam splitter, an upper photodetector and an upper fixed prism, and the upper fixed prism of the upper interferometer is above the upper beam splitter.

[0012] Preferably, the lower interferometer comprises a lower laser light source, a lower beam splitter, a lower photodetector and a lower fixed prism. The lower fixed prism of the lower interferometer is below the lower beam splitter, and the centers of the upper fixed prism, the upper beam splitter, the lower beam splitter and the lower fixed prism are on the same axis as the falling corner cube prism.

[0013] Preferably, the upper photodetector and the lower photodetector convert the optical signal into an electrical signal for output.

[0014] Preferably, the lower interferometer may use a laser interferometer of the gravimeter itself.

[0015] A method for measuring the separation distance between a falling object and a trailer using an absolute gravimeter comprises the following steps:

[0016] S1. Adjust the angles of the lower laser light source and the lower beam splitter of the lower interferometer so that the measuring light enters the bottom of the falling corner cube prism vertically upward. After emitting from the falling body, it is reflected by the lower fixed prism and the lower beam splitter and interferes with the reference photosynthetic beam. The interference signal is received by the lower photodetector.

[0017] S2. Adjust the angles of the laser light source and the upper beam splitter on the upper interferometer so that the measuring light enters vertically downward into the bottom surface of the corner cube prism of the trailer cover, and after being emitted, it is combined with the upper fixed prism and the upper beam splitter to interfere with the reference light, and the interference signal is received by the upper photoelectric detector;

[0018] S3. When the electric control cabinet of the absolute gravimeter controls the falling body to perform free fall motion, the upper photoelectric detector synchronously collects interference signals, and the displacement-time variation data l1=f1(t) of the trailer during the falling process is obtained through calculation, and the lower photoelectric detector in the lower interferometer synchronously collects interference signals, and the displacement-time variation data l2=f2(t) of the falling body during the falling process is obtained through calculation;

[0019] S4, subtract the obtained displacement curve of the trailer from the displacement curve of the falling object to obtain the separation distance curve Δl between the falling object and the trailer during the falling process, Δl = f1(t) - f2(t);

[0020] Furthermore, the start acquisition time of the upper interferometer and the lower interferometer needs to be synchronized during the measurement process;

[0021] Furthermore, the displacement measured by the interferometer is Where λ is the wavelength of the laser light source, N is the number of zero-crossing points in the interference fringes, and the displacement-time curve of the object being measured is obtained by combining the time corresponding to each zero-crossing point.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention adopts a dual interferometer to measure the separation distance between a falling object and a trailer. Since the absolute gravimeter itself carries a laser interferometer for measuring the motion of a falling object, it is only necessary to build a set of interferometers on the top of the vacuum chamber to measure the motion of the trailer. At the same time, a trailer cover carrying a corner cube prism is used. The upper interferometer measures the displacement of the trailer, and the lower interferometer measures the displacement of the falling object. The upper and lower displacements are differentially processed to obtain the separation distance between the falling object and the trailer, thereby completing the measurement of the separation distance between the falling object and the trailer. Compared with the prior art, the entire measurement system has the advantages of simple structure, quick use, and wide applicability.

[0024] 2. The measuring device can measure the separation distance between the falling object and the trailer without interfering with the normal operation of the absolute gravimeter. It can be used to accurately adjust the falling object movement during the installation of the absolute gravimeter, and can also be used for long-term monitoring during experiments to observe the falling of the falling object. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the connection between the metal shell of the absolute gravimeter falling body and trailer separation distance measurement system and the corner cube prism of the trailer cover proposed by the present invention;

[0026] Figure 2 A schematic diagram of the process of measuring the separation distance between a falling object and a trailer by an absolute gravimeter falling object and a trailer separation distance measurement system proposed by the present invention;

[0027] Figure 3 The displacement measurement results of the falling object and the trailer during the falling process, where the blue represents the trailer displacement curve and the red represents the falling object displacement curve;

[0028] Figure 4 It is a schematic diagram of other processes of measuring the separation distance between falling trailers according to the present invention.

[0029] In the figure: 1. metal shell; 2. corner cone prism of trailer cover; 3. trailer cover; 4. falling body; 5. vacuum chamber of absolute gravimeter; 6. upper laser light source; 7. lower laser light source; 8. upper beam splitter; 9. lower beam splitter; 10. upper fixed prism; 11. lower fixed prism; 12. upper photoelectric detector; 13. lower photoelectric detector; 14. first fixed prism; 15. first laser light source; 16. first beam splitter; 17. first reflector; 18. second beam splitter; 19. third beam splitter; 20. first photoelectric detector. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] Example 1

[0032] Reference Figure 1-Figure 3 , a system for measuring the separation distance between a falling object and a trailer of an absolute gravimeter, comprising a vacuum chamber 5 of the absolute gravimeter, a falling object 4 in the vacuum chamber 5 of the absolute gravimeter, a trailer cover 3, and an upper and lower set of interferometers, wherein the upper interferometer and the lower interferometer are respectively arranged at the top and the bottom of the vacuum chamber 5 of the absolute gravimeter, and the falling object 4 is inside the trailer cover 3;

[0033] The trailer cover 3 includes a metal shell 1 and a trailer cover corner cube prism 2. The trailer cover corner cube prism 2 is located inside the metal shell 1 and fixed to the metal shell 1 with the bottom surface facing upward. The trailer cover 3 is fixed on the trailer and moves with the trailer.

[0034] The main component of the falling object 4 is a falling corner cube prism with the bottom surface facing downward. The falling object 4 is placed on a trailer. When the trailer accelerates downward, the falling object 4 separates from the trailer.

[0035] The upper interferometer includes an upper laser light source 6, an upper beam splitter 8, an upper photodetector 12 and an upper fixed prism 10. The upper fixed prism 10 of the upper interferometer is above the upper beam splitter 8.

[0036] The lower interferometer includes a lower laser light source 7, a lower beam splitter 9, a lower photodetector 13 and a lower fixed prism 11. The lower fixed prism 11 of the lower interferometer is below the lower beam splitter 9, and the centers of the upper fixed prism 10, the upper beam splitter 8, the lower beam splitter 9 and the lower fixed prism 11 are on the same axis as the falling corner cube prism.

[0037] The light emitted by the upper laser light source 6 (lower laser light source 7) passes through the upper beam splitter 8 (lower beam splitter 9) and becomes two beams of light, one beam propagates forward, and the other beam is incident vertically upward (downward) into the corner cube prism 3 (falling corner cube prism) of the trailer outer cover, and the outgoing light passes through the upper beam splitter 8 (lower beam splitter 9) and enters the upper fixed prism 10 (lower fixed prism 11), and the outgoing light passing through the upper fixed prism 10 (lower fixed prism 11) is refracted by the upper beam splitter 8 (lower beam splitter 9) and interferes with the light propagating forward, and the two beams of light enter the upper photodetector 12 (lower photodetector 13), and the upper photodetector 12 (lower photodetector 13) converts the optical signal into an electrical signal for output;

[0038] The lower interferometer can use the gravimeter's own laser interferometer.

[0039] The present invention also proposes a method for measuring the separation distance between a falling object and a trailer using an absolute gravimeter, comprising the following steps:

[0040] S1, adjust the angles and positions of the lower laser light source 7, the lower beam splitter 9, the lower fixed prism 11 and the lower photodetector 13 in the lower interferometer, so that the measuring light enters vertically upward into the bottom of the corner cone prism of the falling body 4, and after being emitted from the falling body 4, it is reflected by the lower fixed prism 11 and the lower beam splitter 9 and interferes with the reference photosynthetic beam, and the interference signal is received by the lower photodetector 13;

[0041] S2, adjusting the angles and positions of the upper laser light source 6, the upper beam splitter 8, the upper fixed prism 10 and the upper photodetector 12 in the upper interferometer, so that the measuring light vertically enters the bottom surface of the corner cube prism 3 of the trailer cover downward, and after being emitted from the corner cube prism 3 of the trailer cover, it is reflected by the upper fixed prism 10 and the upper beam splitter 8 and interferes with the reference photosynthetic beam, and the interference signal is received by the upper photodetector 12;

[0042] S3, when the electric control cabinet of the absolute gravimeter controls the falling body 4 to make free fall motion, the upper interferometer and the lower interferometer perform measurements synchronously, and the upper photoelectric detector 12 in the upper interferometer records the interference fringe signal generated by the trailer during the falling process in the vacuum chamber 5 of the absolute gravimeter. After calculation, the displacement-time change data of the trailer during the falling process is obtained: l1=f1(t), where t ＝ is the falling time, l1 is the falling distance of the trailer. The lower photoelectric detector 13 in the lower interferometer records the interference fringe signal generated during the falling process of the falling object 4, and the displacement-time change data of the falling object during the falling process is obtained by calculation l2=f2(t), where t is the falling time, l2 is the falling distance of the falling object 4;

[0043] S4, subtract the obtained displacement curve of the trailer from the displacement curve of the falling object 4 to obtain a separation distance curve Δl=f1(t)-f2(t) between the falling object and the trailer during the falling process;

[0044] S5, Figure 3 It is the result of the separation distance between the falling object 4 and the trailer after one measurement using the method of the present invention.

[0045] Example 2

[0046] The present invention provides a system for measuring the distance between a falling object and a trailer using an absolute gravimeter. Figure 4 , including an absolute gravimeter vacuum chamber 5, a falling object 4 in the absolute gravimeter vacuum chamber 5, and a trailer, on which a first fixed prism 14 is fixed, and the falling object 4 is placed on the trailer, and below the absolute gravimeter vacuum chamber 5 are provided a first laser light source 15, a first beam splitter 16, a first reflecting mirror 17, a second beam splitter 18, a third beam splitter 19, and a first photoelectric detector 20.

[0047] The present invention also provides a method for measuring the separation distance between a falling object and a trailer using an absolute gravimeter, comprising the following steps:

[0048] S1, fix the first fixed prism 14 on the trailer and move it with the trailer, and place the falling object 4 on the trailer and on one side of the first fixed prism 14;

[0049] S2, the light emitted by the first laser light source 15 passes through the first beam splitter 16, and a beam of light vertically enters the first fixed prism 14, and the outgoing light passes through the first reflector 17 and the third beam splitter 19 in turn and enters the first photodetector 20; the other beam of light propagates forward to the second beam splitter 18, and vertically enters the falling object 4 after reflection, and the outgoing light enters the first photodetector 20 after being reflected by the third beam splitter 19. The two beams of light interfere after being combined, and the first photodetector 20 records the interference fringe signal generated during the falling process, and the separation distance between the falling object 4 and the trailer during the falling process is obtained through calculation.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A system for measuring the separation distance between a falling object and a trailer of an absolute gravimeter, comprising a vacuum chamber (5) of the absolute gravimeter, a falling object (4) in the vacuum chamber (5) of the absolute gravimeter, a trailer cover (3), and upper and lower interferometers, characterized in that: The upper interferometer and the lower interferometer are respectively arranged at the top and the bottom of the absolute gravimeter vacuum chamber (5); the falling body (4) is arranged inside the trailer cover (3); the trailer cover (3) comprises a metal shell (1) and a trailer cover corner-cone prism (2); the trailer cover corner-cone prism (2) is located inside the metal shell (1) and is fixed to the metal shell (1) with the bottom facing upward; the trailer cover (3) is fixed to the trailer and moves with the trailer; the falling body (4) mainly comprises a falling body corner-cone prism with the bottom facing downward; the falling body (4) is placed on the trailer; when the trailer accelerates downward, the falling body (4) Separated from the trailer, the upper interferometer comprises an upper laser light source (6), an upper beam splitter (8), an upper photoelectric detector (12) and an upper fixed prism (10), the upper fixed prism (10) of the upper interferometer being located above the upper beam splitter (8), the lower interferometer comprises a lower laser light source (7), a lower beam splitter (9), a lower photoelectric detector (13) and a lower fixed prism (11), the lower fixed prism (11) of the lower interferometer being located below the lower beam splitter (9), and the centers of the upper fixed prism (10), the upper beam splitter (8), the lower beam splitter (9) and the lower fixed prism (11) are on the same axis as the falling corner cube prism.

2. The absolute gravimeter falling object and trailer separation distance measurement system according to claim 1, characterized in that: The upper photodetector (12) and the lower photodetector (13) convert optical signals into electrical signals for output.

3. The absolute gravimeter falling object and trailer separation distance measurement system according to claim 1, characterized in that: The lower interferometer uses the gravimeter's own laser interferometer.

4. A method for measuring the separation distance between a falling object and a trailer using an absolute gravimeter, used to implement the system described in any one of claims 1 to 3, characterized in that: The following steps are involved: S1, adjusting the angles of the lower laser light source (7) and the lower beam splitter (9) of the lower interferometer so that the measuring light enters the bottom of the corner cone prism of the falling object (4) vertically upward, and after being emitted from the falling object (4), it is reflected by the lower fixed prism (11) and the lower beam splitter (9) and interferes with the reference photosynthetic beam, and the interference signal is received by the lower photoelectric detector (13); S2, adjusting the angles of the laser light source (6) and the upper beam splitter (8) on the upper interferometer so that the measuring light enters vertically downward into the bottom surface of the corner cube prism (2) on the trailer cover, and after being emitted, it is combined with the upper fixed prism (10) and the upper beam splitter (8) to interfere with the reference light, and the interference signal is received by the upper photoelectric detector (12); S3. When the electric control cabinet of the absolute gravimeter controls the falling body to perform free fall motion, the upper photoelectric detector (12) synchronously collects interference signals, and calculates the displacement-time variation data of the trailer during the falling process. l 1 =f 1 (t) The lower photoelectric detector (13) in the lower interferometer synchronously collects interference signals, and the displacement-time variation data of the falling object (4) during the falling process are obtained through calculation. l 2 =f 2 (t) ; S4. Subtract the displacement curve of the trailer from the displacement curve of the falling object (4) to obtain the separation distance curve between the falling object and the trailer during the falling process. Δl, ； Furthermore, the start acquisition time of the upper interferometer and the lower interferometer needs to be synchronized during the measurement process; Furthermore, the displacement measured by the interferometer is , where λ is the wavelength of the laser source, N is the number of zero-crossing points in the interference fringes. Combined with the time corresponding to each zero-crossing point, the displacement-time curve of the measured object is obtained.

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