CN107121708A - Absolute gravity measurement system and measuring method - Google Patents

Abstract

The invention provides an absolute gravity measurement system and a measurement method. The absolute gravity measurement includes: a free fall device, a laser interferometric measurement device, and a vibration isolation platform. The free-fall device includes a housing, a vacuum chamber arranged in the housing, and a power device connected in transmission with the vacuum chamber. The power device is used to control the movement of the vacuum chamber in the vertical direction. The falling body is arranged in the vacuum chamber. The bottom of the vacuum chamber is provided with a vacuum chamber observation window for observing the free fall motion of the falling body. The absolute gravity measurement system further includes a vacuum chamber displacement measurement device arranged in the housing. The vacuum chamber displacement measuring device includes a grating scale arranged inside the housing, and a reading head fixedly installed on the outer shell of the vacuum chamber. The absolute gravimetric measurement system further includes an air refractive index measurement device for measuring the air refractive index inside the housing.

Description

Absolute gravity measurement system and measurement method

technical field

The invention relates to the technical field of precision instruments, in particular to an absolute gravity measurement system and a measurement method.

Background technique

Absolute gravimeter is an instrument that calculates the absolute value of gravitational acceleration by measuring the response of sensitive elements to the gravitational field. It undertakes important measurement tasks in the fields of metrology, surveying and mapping, seismic, geophysics, resource exploration and auxiliary navigation. Absolute gravimeters can be divided into two categories according to the linearity of sensitive components: one is the classic free fall absolute gravimeter, which uses the laser wavelength as the reference reference for length measurement, the atomic clock frequency as the reference reference for time measurement, and the angular reflective prism as the sensitive element , using a Mach-Zehnder type laser interferometer to measure the displacement of a corner reflective prism in free fall in vacuum. Every time the falling prism moves a distance of one-half of the laser wavelength, the light intensity detected by the photodetector will change for a full period. The photodetector converts the optical signal into an electrical signal with an average value of zero, and by measuring the zero-crossing time, the trajectory of the falling object can be deduced, and the value of the acceleration of gravity can be solved by fitting. The other is the atomic interference absolute gravimeter, which uses the response of the atomic energy level distribution probability to the gravitational field to measure the gravitational acceleration value.

Due to the relatively late maturity and high complexity of atomic interference gravimeter technology, the most widely used absolute gravimeter is still the classic free-fall absolute gravimeter. Micro-g LaCoste developed the FG-5 Absolute Gravimeter based on the earlier JILA Absolute Gravimeter. The gravimeter adopts the "no-drag falling cavity technology" to effectively reduce the influence of residual air, and places the reference prism in the laser interferometer in the "Super Spring" to form a vibration isolation system to reduce ground vibration. Effect of vibration on measurement results. In addition, the vibration isolation system of the gravimeter is arranged in line with the vacuum falling chamber, which meets Abbe's principle and can improve measurement accuracy and reliability. The FG-5X absolute gravimeter developed on this basis has a compensating mass, which can reduce the impact of the ground rebound effect on the measurement results. Both instruments have an uncertainty of up to 2 µGal. In addition, the IMGC-02 absolute gravimeter developed by the Italian National Institute of Metrology (INRIM) adopts the motion method of throwing up and down, and the uncertainty can reach 9μGal. The NIM series of absolute gravimeters developed by the China Institute of Metrology has participated in international absolute gravimeter comparisons for many times, and the uncertainty is better than 10μGal. In 2011, our research group independently developed the T-1 high-precision absolute gravimeter. The gravimeter also adopts the classic free-fall structure, uses the elastic pull-down method to realize the release of the falling body, and uses the high-speed signal acquisition system to collect the output signal of the miniaturized laser interferometer, and the uncertainty can reach the μGal level. In order to improve the mobility of the instrument, Micro-g has also developed a portable absolute gravity meter A-10. The gravimeter simplifies the overall structure of the system by reducing the vacuum chamber and vibration isolation system, simplifying the laser interferometer, and selecting a small ion pump instead of the original ion pump. It can be quickly disassembled and easily moved between measurement locations. The A-10 Portable Absolute Gravimeter has an accuracy of up to 10μGal.

In all the above-mentioned absolute gravimeters, the falling process of the falling body all takes place in a large vacuum chamber, and generally has an ion pump to maintain the vacuum in the chamber to reduce the impact of air damping, air buoyancy, etc. on the falling body. movement interference. These absolute gravimeters can achieve high-precision measurements in a laboratory environment, but their systems are complex and heavy, and are not suitable for field measurements in harsh environments.

For this reason, it is necessary to design an absolute gravimeter that is lighter, simpler, more maneuverable and more reliable. Although the above-mentioned A-10 portable absolute gravimeter is smaller in size than other gravimeters, because it still uses the traditional structure, the volume reduction is limited, and an ion pump is still needed to maintain the vacuum during transportation. In emergencies such as power outages, there is a risk of vacuum leakage.

Contents of the invention

Based on this, it is necessary to address the above technical problems and provide an absolute gravity measurement system and measurement method that are light, simple, more maneuverable and more reliable, and suitable for field measurements in harsh environments.

An absolute gravimetric measurement system comprising:

The free fall device is used to realize the free fall motion of the falling body;

A laser interferometry device, used to track the falling body for free-fall motion to obtain laser interference fringe signals;

The vibration isolation platform is arranged between the free fall device and the laser interferometry device, and is used to isolate the influence of ground vibration on the measurement, wherein:

The free fall device includes a housing, a vacuum chamber arranged in the housing, and a power device connected to the vacuum chamber in transmission, and the power device is used to control the movement of the vacuum chamber in the vertical direction, so The falling body is arranged in the vacuum chamber, and the bottom of the vacuum chamber is provided with a vacuum chamber observation window for observing the free fall movement of the falling body;

The absolute gravity measurement system further includes a vacuum chamber displacement measuring device arranged in the housing, the vacuum chamber displacement measuring device includes a grating ruler arranged inside the housing, and a reading head;

The absolute gravimetric measurement system further includes an air refractive index measurement device for measuring the air refractive index inside the housing.

In one of the embodiments, the free fall device includes a support frame arranged inside the housing, and the support frame includes a vertically arranged linear guide rail;

The vacuum chamber is slidably installed on the linear guide rail, and is driven by the power device to move along the linear guide rail;

The grating ruler is installed on the support frame, and is arranged in parallel with the linear guide rail so that the grating ruler is opposite to the reading head.

In one of the embodiments, the inner wall of the vacuum chamber is fixedly provided with a supporting structure for supporting the falling body.

In one embodiment, the vacuum chamber is sealed by welding, and the vacuum degree in the vacuum chamber is 10 ^-6 Pa to 10 ^-4 Pa.

In one of the embodiments, an air absorbent is arranged in the vacuum chamber.

In one of the embodiments, a first reflective prism is arranged in the falling body, which is used to reflect the measuring laser light emitted by the laser interferometry device;

A second reflective prism is arranged inside the shock-isolation platform for reflecting the measuring laser light reflected by the first reflective prism.

In one of the embodiments, the laser interferometry device includes:

The first light splitting element is used to split the collimated laser light into the test laser light and the reference laser light perpendicular to each other, the test laser light is transmitted to the first reflective prism, and is reflected to the second reflective prism through the first reflective prism. reflective prism;

a second beam splitter, configured to photosynthesize the reference laser light passing through the second beam splitter and the test laser light reflected to the second beam splitter through the second reflective prism;

The photodetector is used to convert the interference fringes formed by the measurement laser light combined with the reference laser light through the second beam splitter into an analog signal.

In one of the embodiments, the air refractive index measuring device includes a sensor disposed inside the housing, and the sensor is used to sense the temperature, air pressure and humidity inside the housing.

In one of the embodiments, the absolute gravimetric measurement system also includes:

A digital signal processor, the digital signal processor is electrically connected to the power device and the sensor, and is used to control the power device, and collect the temperature, air pressure and humidity inside the housing through the sensor;

A computer connected to the digital signal processor, used to send instructions to the power device through the digital signal processor to control the power device, and according to the information sent back by the digital signal processor inside the housing Calculate the air refraction index inside the housing according to the temperature, air pressure and humidity;

A data acquisition card connected with the vacuum chamber displacement measurement device, the laser interference device and the computer, and the computer obtains the laser interference fringe signal and the vacuum chamber position signal emitted by the laser interference device through the data acquisition card. Vacuum chamber displacement signals from the displacement measuring device; and

An atomic clock connected to the data acquisition card, the atomic clock provides a standard clock reference signal for the data acquisition card.

An absolute gravimetric measurement method using the absolute gravimetric measurement system described in any one of the above embodiments, comprising:

Controlling the vacuum chamber to move vertically downward from the top of the casing through the power device, so that the falling body can freely fall;

Tracking the falling body through the laser interferometry device for free-fall motion to obtain laser interference fringe signals;

The displacement signal of the vacuum chamber when the vacuum chamber falls is measured by the vacuum chamber displacement measuring device;

measuring the refractive index of air inside the casing by the air refractive index measuring device; and

The absolute gravitational acceleration is calculated according to the laser interference fringe signal, the vacuum chamber displacement signal and the air refractive index.

The absolute gravity measurement system of the present application can work without the ion pump, which simplifies the absolute gravity measurement system and improves the convenience and reliability of the absolute gravity measurement field operation. In addition, the technical solution of the present application also includes a vacuum chamber displacement measuring device and an air refractive index measuring device, so that the displacement information of the vacuum chamber measured by the vacuum chamber displacement measuring device and the inside of the housing measured by the air refractive index measuring device can be The refractive index of air is corrected for the measurement method of absolute gravity, so as to obtain more accurate measurement results. Therefore, the absolute gravimetric measurement system of the present application has the advantages of portability and simplicity, higher mobility and reliability, and is suitable for field measurement in harsh environments.

Description of drawings

Fig. 1 is the structural representation of the absolute gravimetric measurement system of an embodiment of the present invention;

Fig. 2 is the front view of the internal structure of the free fall device of the absolute gravimetric measurement system in one embodiment of the present invention;

Fig. 3 is a side view of the internal structure of the free-fall device in Fig. 2;

Fig. 4 is a schematic diagram of the internal structure of the vacuum chamber of the absolute gravity measurement system in one embodiment of the present invention;

Fig. 5 is a schematic diagram of the optical path structure of the laser interferometry device of the absolute gravity measurement system in one embodiment of the present invention;

Fig. 6 is the structural block diagram of the absolute gravimetric measurement system in one embodiment of the present invention;

Fig. 7 is a schematic diagram of the free-fall trajectory measurement of the absolute gravity measurement system in one embodiment of the present invention.

Description of main component symbols

Absolute Gravity Measurement System 100

Free Fall Device 10

Top flange 11

Shell 12

main chamber 13

bottom viewing window 14

Bottom flange 15

Vibration isolation platform 20

Laser interferometry device 30

Collimated lasers 31

reflective elements 32

The first light splitting element 33

Second light splitting element 34

lens 35

Photodetector 36

Digital Signal Processor 40

computer 50

Data Acquisition Card 60

atomic clock 70

Vacuum chamber 110

Copper pipe 111

Falling 112

Vacuum chamber roof 113

First reflector prism 114

Vacuum from bin floor 115

Support structure 116

Vacuum chamber observation window 117

Vacuum chamber side wall 119

Vacuum chamber displacement measuring device 120

Grating ruler 122

Readhead 124

Mount 126

Air Refractive Index Measuring Device 130

Power unit 140

Controlling Motors 142

Flexible Couplings 143

timing belt 144

Travel switch 145

The first timing pulley 146

Second timing pulley 148

Support frame 150

Frame top plate 151

Rail bracket 152

Linear guides 154

slider 155

Vacuum chamber connector 156

Frame bottom plate 157

Second reflective prism 214

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Please refer to FIG. 1 , an embodiment of the present invention provides an absolute gravity measurement system 100 for measuring absolute gravity values at different positions on the earth. The absolute gravity measurement system 100 includes a free fall device 10 , a vibration isolation platform 20 , a laser interferometry device 30 , a vacuum chamber displacement measurement device 120 and an air refractive index measurement device 130 .

The free fall device 10 is arranged on the vibration isolation platform 20 for realizing the free fall movement of the falling body 112 . The free fall device 10 includes a casing 12 , a vacuum chamber 110 disposed in the casing 12 , and a power device 140 connected to the vacuum chamber 110 in transmission. The falling body 112 is disposed in the vacuum chamber 110 . The power device 140 can control the vacuum chamber 110 to move in the direction of gravity, so as to realize the free-fall movement of the falling body 112 . The inside of the housing 12 is atmospheric pressure. It can be understood that the bottom of the casing 12 also has a bottom observation window 14 , which can allow laser light to enter to detect the falling object 112 .

The vibration isolation platform 20 is arranged between the free fall device 10 and the laser interferometry device 30 for isolating the influence of the vibration of the bottom surface on the measurement. The laser interferometry device 30 can emit a measuring laser, and track the falling body 112 through the measuring laser, so as to obtain the laser interference fringe signal of the falling body 112 when it is in free fall. The vacuum chamber displacement measuring device 120 is used to measure the vacuum chamber displacement signal when the vacuum chamber 110 falls. The vacuum chamber displacement measuring device 120 includes a grating ruler 122 disposed inside the housing 12 , and a reading head 124 fixedly installed on the outer shell of the vacuum chamber 110 . The air refractive index measuring device 130 is disposed inside the housing 12 for measuring the air refractive index inside the housing 12 .

Referring to FIGS. 2-3 , the housing 12 can be composed of a top flange 11 , a main cavity 13 , a bottom flange 15 and a bottom observation window 14 . Wherein, the top flange 11 , the main cavity 13 and the bottom flange 15 can be made of aluminum alloy material for reducing the weight of the free fall device 10 . It can be understood that the materials of the top flange 11 , the main cavity 13 and the bottom flange 15 are not limited to aluminum alloy, and other metal materials can also be used. It can be understood that the structural shape of the housing 12 is not limited, as long as a storage space can be formed.

In one embodiment, a support frame 150 may be provided inside the free fall device 10 for installing the vacuum chamber 110 . The support frame 150 includes a frame top plate 151 , a rail bracket 152 and a frame bottom plate 157 . The rail bracket 152 is fixed between the frame top plate 151 and the frame bottom plate 157 . The guide rail bracket 152 is provided with a linear guide rail 154 . The vacuum chamber 110 is slidably disposed on the linear guide rail 154 so as to be able to slide along the linear guide rail 154 . It can be understood that the linear guide rail 154 can be matched with a sliding block 155 . The slider 155 can move linearly along the linear guide rail 154 . The vacuum chamber 110 can be fixed on the slider 155 through a vacuum chamber connecting piece 156 . Therefore, under the control of the power device 140 , the vacuum chamber 110 can move linearly along the linear guide rail 154 to realize the free-fall motion of the falling body 112 .

The grating scale 122 can be fixedly mounted on the supporting frame 150 . Specifically, two ends of the grating ruler 122 may be respectively fixed to the frame top plate 151 and the frame bottom plate 157 . The grating ruler 122 is arranged parallel to the linear guide rail 154 at intervals. The reading head 124 is disposed on the vacuum chamber 110 . Specifically, the reading head 124 can be fixed on the vacuum chamber 110 through a connecting piece 126 . Therefore, the movement of the reading head 124 relative to the grating ruler 122 is the movement of the vacuum chamber 110 relative to the supporting frame 150 . Thus the displacement of the reading head 124 is equivalent to the displacement of the vacuum chamber 110 . Therefore, the vacuum chamber displacement measuring device 120 can measure the displacement information of the vacuum chamber 110 through the grating ruler 122 and the reading head 124 , that is, the vacuum chamber displacement information. It can be understood that the measurement range of the grating ruler 122 should be greater than the maximum speed of the vacuum chamber 110 . The instantaneous acceleration of the vacuum chamber 110 may be greater than the acceleration of gravity. In one embodiment, the grating ruler 122 can continuously output a 0V square wave or a 5V square wave, and the measurement resolution is 2×10 ⁻⁶ m.

The power device 140 can be any device capable of providing power, as long as it can control the vertical movement of the vacuum chamber 110 in the direction of gravity. The function of the power device 140 is to provide power to control the movement of the vacuum chamber 110 along the linear track 154 . In one embodiment, the power device 140 includes a control motor 142 , a flexible coupling 143 , a synchronous belt 144 , a travel switch 145 , a first synchronous pulley 146 and a second synchronous pulley 148 . The control motor 142 can pass through the casing 12 and be installed on the support frame 150 . The rotating shaft of the control motor 142 is connected with the flexible coupling 143 . The flexible coupling 143 is connected with the first synchronous pulley 146 . The first synchronous pulley 146 is installed on the frame top plate 151 . The second synchronous pulley 148 is mounted on the frame bottom plate 147 . The synchronous belt 12 is wound on the first synchronous pulley 146 and the second synchronous pulley 148 , and is fixedly connected with the vacuum chamber connector 156 . The control motor 142 can drive the vacuum chamber connector 156 to move through the first synchronous pulley 146 and the synchronous belt 144, thereby realizing the rise and fall of the vacuum chamber 110 and the free movement of the falling body 112. whereabouts. The travel switch 145 is fixedly installed on the track bracket 152 . After the vacuum chamber connector 156 contacts the travel switch 145, the control motor 142 stops rotating.

Referring to FIG. 4 , in one embodiment, the vacuum chamber 110 includes a copper pipe 111 , a vacuum chamber roof 113 , a vacuum chamber sidewall 119 , a vacuum chamber bottom 115 , and a vacuum chamber observation window 117 . The vacuum chamber side wall 119 is arranged between the vacuum chamber top plate 113 and the vacuum chamber bottom plate 115, and the three together form a closed vacuum chamber. The falling body 112 is placed in the vacuum chamber. The copper tube 11 is used to evacuate the vacuum cavity. The vacuum chamber top plate 113 , the vacuum chamber side wall 119 , and the vacuum chamber bottom plate 115 can be sealed together by welding. The vacuum chamber viewing window 117 is disposed on the vacuum chamber bottom plate 115 . Laser light can enter the interior of the vacuum chamber 110 through the vacuum chamber observation window 117 . It can be understood that the vacuum chamber viewing window 117 and the vacuum chamber bottom plate 115 can also be sealed and connected together by welding. It can be understood that the material of the vacuum chamber 110 should have a certain strength and be suitable for a vacuum chamber, it can be but not limited to metal. In one embodiment, the vacuum chamber 110 is made of aluminum alloy. A supporting structure 116 may also be provided on the inner wall of the vacuum chamber 110 for supporting the falling body 112 . It can be understood that grooves can also be provided on the supporting structure 11 to cooperate with the protruding structures provided on the falling body 112 , so that the falling body 112 can be stably placed on the supporting structure 116 . In one embodiment, the support structure 116 is a support ring. The falling body 112 is placed on the support ring. A first reflective prism 114 is also arranged inside the falling body 112 . The first reflective prism 114 can reflect the laser light incident from the observation window 117 of the vacuum chamber for measurement. It can be understood that the structure of the first reflective prism 114 is not limited and can be selected according to requirements.

The vibration isolation platform 20 can be composed of mechanical springs and a precision control system to achieve an intrinsic oscillation period of more than 20 seconds, which has a better effect of isolating ground vibrations. The vibration isolation platform 20 can be suspended with a second reflective prism 214, which is used to cooperate with the laser interferometry device 30 to form an optical path, and emit the laser light reflected by the first reflective prism 114 of the falling body 112 to the laser beam. Interferometry device 30 . It can be understood that the structure of the second reflective prism 214 is not limited and can be selected according to needs.

The laser interferometry device 30 is used to measure the laser interference fringe signal of the falling body 112 in free fall. The laser interference fringe signal is used to calculate the absolute gravitational acceleration of the falling object 112 . It can be understood that the structure of the laser interferometry device 30 is not limited, as long as the above functions can be realized. Please also refer to FIG. 5 , in one embodiment, the laser interferometry device 30 may include a collimated laser 31, a reflective element 32, a first light splitting element 33, a second light splitting element 34, a lens 35, and a photodetector 36. The collimated laser 31 is used to emit collimated laser light, which may be composed of a laser and a collimator. The reflective element 32 is used to reflect the collimated laser light emitted by the collimated laser 31 into the first light splitting element 33 . It can be understood that when the collimated laser light directly enters the first light splitting element 33, the reflective element 32 is an optional element. The first light splitting element 33 can divide the collimated laser light into a test laser light and a reference laser light. The test laser and the test laser are perpendicular to each other. The test laser is input into the first reflective prism 114 and reflected to the second light splitting element 34 through the first reflective prism 114 . The reference laser light enters the second light splitting element 34 , combines with the test laser light and enters the photodetector 36 . The reference laser light and the test laser light passing through the second light splitting element 34 may enter the photodetector 36 after passing through the lens 35 . The photodetector 36 can convert the interference fringes formed by the measurement laser light combined with the reference laser light through the second light splitting element 34 into an analog signal. It can be understood that the lens 35 can also be an optional element. Both the first beam splitting element 33 and the second beam splitting element 34 can be beam splitters.

Referring to FIG. 6 , the absolute gravity measurement system 100 may further include a digital signal processor 40 , a computer 50 connected to the digital signal processor 40 , a data acquisition card 60 , and an atomic clock 70 . The digital signal processor 40 is electrically connected with the power device 140 and the air refractive index measurement device 130 . The digital signal processor 40 is used to control the power device 140 , and collect the temperature, air pressure and humidity inside the housing 12 through the air refractive index measuring device 130 . The computer 50 is used to send instructions to the power unit 140 through the digital signal processor 40 to control the power unit 140 , and according to the temperature inside the casing 12 returned by the digital signal processor 40 , air pressure and humidity to calculate the refractive index of the air inside the casing 12 . The data acquisition card 60 is electrically connected with the vacuum chamber displacement measurement device 120 , the laser interference device 130 and the computer 50 . The computer 50 obtains the laser interference fringe signal from the laser interference device 30 and the vacuum chamber displacement signal from the vacuum chamber displacement measuring device 120 through the data acquisition card 60 . The atomic clock 70 is connected to the data acquisition card 60 , and the atomic clock 70 provides a standard clock reference signal for the data acquisition card 60 . The atomic clock 70 can be any reference clock, such as rubidium atomic clock. The digital signal processor 40 can use any form of embedded processor.

How the free-fall device 10 realizes the free-fall movement of the falling body 112 will be described in detail below.

(1), through the rotation of the control motor 142, the vacuum chamber connector 156 moves upward, and drives the vacuum chamber 110 to move upward, thereby transporting the vacuum chamber 110 and the falling body 112 placed therein to the top position of the housing 12.

(2) After the vacuum chamber connector 156 contacts the travel switch 145 , the control motor 142 stops rotating.

(3) Through the reverse rotation of the control motor 142 , the vacuum chamber connecting member 156 moves downward. The vacuum chamber 110 moves downward with the acceleration of the vacuum chamber connecting member 156 . The motion acceleration of the vacuum chamber 110 is greater than the gravitational acceleration. The falling body 112 is separated from the supporting structure 116, and at this moment, the falling body 112 is only subjected to the action of gravity, and starts to freely fall downward.

(4) When the vacuum chamber 110 moves down to the bottom position of the casing 12 , the control motor 10 decelerates. The support structure 116 reconnects with the falling body 112 in free fall, and together they decelerate until they come to a standstill.

(5), repeating the above steps (1)-(4), the free fall movement of the falling body 112 can be realized repeatedly.

Compared with the prior art, the technical proposal of the present application adopts the high vacuum maintenance technology, maintains the vacuum degree in the miniaturized vacuum chamber through the welding and sealing technology, and skillfully realizes the free fall movement of the falling body. The adoption of a miniaturized vacuum chamber allows the gravimeter to work without the ion pump, which simplifies the absolute gravity measurement system and improves the convenience and reliability of absolute gravity measurement in field operations. In addition, the technical solution of the present application also includes a vacuum chamber displacement measuring device and an air refractive index measuring device, so that the displacement information of the vacuum chamber measured by the vacuum chamber displacement measuring device and the inside of the housing measured by the air refractive index measuring device can be The refractive index of air is corrected for the measurement method of absolute gravity, so as to obtain more accurate measurement results. Therefore, the absolute gravimetric measurement system of the present application has the advantages of portability and simplicity, higher mobility and reliability, and is suitable for field measurement in harsh environments.

The embodiment of the present application also provides an absolute gravity measurement method using the absolute gravity measurement system 100, including:

The vacuum chamber 110 is controlled by the power device 140 to move vertically downward from the top of the casing 12, so that the falling body 112 is free-falling;

Tracking the falling body 112 through the laser interferometry device 30 for free-fall motion to obtain laser interference fringe signals;

The vacuum chamber displacement signal when the vacuum chamber 110 falls is measured by the vacuum chamber displacement measuring device 120;

Measure the air refractive index inside the housing 12 by the air refractive index measuring device 130; and

The absolute gravitational acceleration is calculated according to the laser interference fringe signal, the vacuum chamber displacement signal and the air refractive index.

The following describes how to calculate the absolute gravitational acceleration by using the laser interference fringe signal, the vacuum chamber displacement signal and the air refractive index. In one falling cycle, the vacuum chamber 110 falls together with the falling body 112 . During the falling process, the displacement of the falling body 112 relative to the vacuum chamber 110 and the displacement of the vacuum chamber 110 relative to the laser interferometry device 30 both change. The above changes will lead to changes in the optical path of the measuring arm. At this time, the laser interference fringe signal can no longer represent the absolute value of the displacement of the falling object 112, but the trajectory of the falling object 112 should be reconstructed by analyzing the optical path change of the measuring arm. Specifically The process is as follows.

Please refer to FIG. 7 , which shows the positional relationship between the vacuum chamber 110 and the falling body 112 at time i (solid line) and time i+1 (dotted line) during the falling process. The rectangle represents the vacuum chamber 110 , and the right triangle represents the first corner reflective prism 114 inside the falling body 112 . Arrows represent the measuring arm beam at time i (solid line) and time i+1 (dashed line). x is the displacement of the falling body 112, and y is the displacement of the vacuum chamber of the vacuum chamber 110, both of which take the vertical downward as the positive direction, and the subscript i represents their respective values at the moment i. Record the optical path of the measuring arm as z, then the change of z from time i to time i+1 is:

z _i+1 -z _i ＝2(y _i+1 -y _i )(n _TPf -n _vac )+2( _{xi +1} -xi )n _vac (1)

In the formula, n _TPf represents the refractive index of the air near the measuring arm of the laser interferometer, and n _vac is the refractive index of the residual gas in the vacuum chamber. It can be seen from formula (1) that by measuring the displacement y of the vacuum chamber, the air refractive index n _TPf and the laser interference fringe signal z, the free fall trajectory x in vacuum can be reconstructed. These three physical quantities are respectively obtained by the laser interferometry device 30 , the vacuum chamber displacement measurement device 120 and the air refractive index measurement device 130 of the absolute gravity measurement system 100 . Therefore, the accurate free-fall trajectory of the falling body 112 can be calculated through the above three physical quantities, thereby calculating the absolute gravitational acceleration.

Since the vacuum chamber 110 described in this application falls together with the falling body 112, according to the formula (1), the laser optical path change measured by the laser interferometry device 35 is no longer equal to the free fall displacement of the falling body . By installing the vacuum chamber displacement measurement device 120 and the air refractive index measurement device 130 in the free fall device 10 to cooperate with the laser interferometry device 30, the accuracy of the measurement results can be guaranteed.

In the several embodiments provided by the present invention, it should be understood that the disclosed related devices and methods may be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the modules or units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be Incorporation may either be integrated into another system, or some features may be omitted, or not implemented. In another point, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium, as described in the present invention. In an embodiment, the program may be stored in a storage medium of a computer system, and executed by at least one processor in the computer system, so as to implement the processes of the embodiments including the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM), and the like.

The above-mentioned embodiments only express several implementation modes of the present invention, and the accompanying descriptions are more specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. a kind of absolute gravity measurement system, including：

Freely falling body device, the movement of falling object for realizing falling bodies；

Laser-interfering measurement device, the movement of falling object is made to obtain laser interferencefringes signal for tracking the falling bodies；

Vibration-isolating platform, is arranged between the freely falling body device and the laser-interfering measurement device, for isolating ground shake The dynamic influence to the measurement, it is characterised in that：

The freely falling body device includes housing, the vacuum storehouse being arranged in the housing and is driven with the vacuum storehouse to connect The power set connect, the power set are used to control the vacuum storehouse in the motion of vertical direction, and the falling bodies are arranged at institute State in vacuum storehouse, the vacuum orlop portion is provided with the movement of falling object that vacuum storehouse observation window is used to observe the falling bodies；

The absolute gravity measurement system further comprises the vacuum position in storehouse measuring system being arranged in the housing, described true Hole capital after selling all securities displacement measuring device includes the grating scale for being arranged at the enclosure interior, and is fixedly mounted on vacuum storehouse shell Reading head；

The absolute gravity measurement system further comprises measuring device of refraction index of air, the sky for measuring the enclosure interior Gas refractive index.

2. absolute gravity measurement system as claimed in claim 1, it is characterised in that the freely falling body device includes being arranged at The support frame of the enclosure interior, the support frame includes the line slideway being vertically arranged；

The vacuum storehouse is slidably mounted on the line slideway, and line slideway described in the driving lower edge in the power set is moved It is dynamic；

The grating scale is installed on the support frame, and is set so that the grating with the line slideway parallel interval Chi is oppositely arranged with the reading head.

3. absolute gravity measurement system as claimed in claim 1, it is characterised in that vacuum storehouse inwall is fixedly installed branch Support structure, for supporting the falling bodies.

4. absolute gravity measurement system as claimed in claim 1, it is characterised in that the vacuum storehouse is welded seal, described Vacuum in vacuum storehouse is 10^-6Pa to 10^-4Pa。

5. absolute gravity measurement system as claimed in claim 4, it is characterised in that air absorption is provided with the vacuum storehouse Agent.

6. absolute gravity measurement system as claimed in claim 1, it is characterised in that

The first reflecting prism is provided with the falling bodies, for reflecting the measurement laser that the laser-interfering measurement device is sent；

The second reflecting prism is provided with the shock insulation platform, the measurement for reflecting the first reflecting prism reflection swashs Light.

7. absolute gravity measurement system as claimed in claim 6, it is characterised in that the laser-interfering measurement device includes：

First beam splitter, for collimation laser to be divided into the orthogonal testing laser and reference laser, the test Laser Transmission reflexes to second reflecting prism to first reflecting prism, and by first reflecting prism；

Second spectroscope, for described second spectroscopical reference laser will to be passed through, and via second reflecting prism Reflex to described second spectroscopical testing laser progress photosynthetic；

Photodetector, for by via the photosynthetic measurement laser of second spectroscope and reference laser formation Interference fringe is converted into analog signal.

8. absolute gravity measurement system as claimed in claim 1, it is characterised in that the measuring device of refraction index of air includes The sensor of the enclosure interior is arranged at, the sensor is used for temperature, air pressure and the humidity for sensing the enclosure interior.

9. absolute gravity measurement system as claimed in claim 8, it is characterised in that also include：

Digital signal processor, the digital signal processor is electrically connected with the power set and the sensor, for controlling The power set are made, and pass through temperature, air pressure and the humidity of the sensor collection enclosure interior；

The computer being connected with the digital signal processor, for giving the power set by the digital signal processor Instruction is sent to control the power set, and the temperature for the enclosure interior passed back according to the digital signal processor Degree, air pressure and humidity calculate the air refraction of the enclosure interior；

The data collecting card being connected with the vacuum position in storehouse measuring system, the laser interference device and the computer, institute State computer and laser interferencefringes signal that the laser interference device sends is obtained and described true by the data collecting card The vacuum position in storehouse shifting signal that hole capital after selling all securities displacement measuring device is sent；And

The atomic clock being connected with the data collecting card, the atomic clock provides the clock reference of standard for the data collecting card Signal.

10. a kind of absolute gravity measurement method of absolute gravity measurement system using as described in claim any one of 1-9, bag Include：

The vacuum storehouse is controlled to be moved straight down by the case top by the power set, so that the falling bodies Do the movement of falling object；

Do the movement of falling object to obtain laser interferencefringes signal by the laser-interfering measurement device tracking falling bodies；

Vacuum position in storehouse shifting signal when the vacuum storehouse falls is measured by the vacuum position in storehouse measuring system；

The air refraction of the enclosure interior is measured by the measuring device of refraction index of air；And

Absolute gravity is calculated according to the laser interferencefringes signal, the vacuum position in storehouse shifting signal and the air refraction to add Speed.