阅读说明：本技术 一种基于fpga的激光对管重力检测仪及检测方法 (FPGA-based laser pair tube gravity detector and detection method ) 是由 刘三军 杨俊红 来国红 孙先波 徐建 于 2020-05-25 设计创作，主要内容包括：本发明属于重力检测技术领域,公开了一种基于FPGA的激光对管重力检测仪及检测方法,FPGA与电气压传感器、LCD显示屏、Wifi模块、按键和接收器电连接；电源通过导线与FPGA、电磁继电器、电磁铁、发射器连接；FPGA与电磁继电器电连接,电磁继电器与电磁铁电连接,电磁铁下端放置有小球。本发明利用FPGA内部恒温晶振产生高达200MHz的时钟对激光对管的触发时刻进行精确检测,使得时间测量的精度可以达到5纳秒；采用最小二乘法计算重力加速度,该算法对小球的初始速度、位置以及电磁继电器的反应时间不敏感,提高了测量的精度。本发明对系统精度进行分析使得整个系统具有精度高、操作简单、性价比高等特点。(The invention belongs to the technical field of gravity detection, and discloses a laser geminate transistor gravity detector and a detection method based on an FPGA (field programmable gate array). the FPGA is electrically connected with an electric voltage sensor, an LCD (liquid crystal display), a Wifi (wireless fidelity) module, a key and a receiver; the power supply is connected with the FPGA, the electromagnetic relay, the electromagnet and the emitter through leads; FPGA is connected with electromagnetic relay electricity, and electromagnetic relay is connected with the electro-magnet electricity, and the bobble has been placed to the electro-magnet lower extreme. According to the invention, a clock with the frequency of 200MHz generated by a constant-temperature crystal oscillator in the FPGA is used for accurately detecting the triggering time of the laser geminate transistor, so that the time measurement precision can reach 5 nanoseconds; the gravity acceleration is calculated by adopting a least square method, and the algorithm is insensitive to the initial speed and position of the small ball and the reaction time of the electromagnetic relay, so that the measurement precision is improved. The invention analyzes the system precision, so that the whole system has the characteristics of high precision, simple operation, high cost performance and the like.)

1. The FPGA-based laser pair tube gravity detection method is characterized by comprising the following steps of:

firstly, extracting air from a container by using a vacuum pump, displaying the pressure in an air pressure sensor acquisition system controlled by an FPGA on an LCD screen, and controlling the vacuum pump;

after the interior of the container becomes vacuum, the electromagnetic relay is controlled to release the small balls through connection of the mobile phone APP and a WiFi module of the FPGA or directly through keys on the FPGA;

step three, when the FPGA receives a control instruction of a mobile phone or a key, the CPU controls the electromagnetic relay to release the small balls, starts a high-speed clock in the FPGA, starts an internal counter to start counting, the counting value starts from 0, the counting value of the rising edge of each clock is automatically increased by 1, and when the small balls fall to the nth laser pair tube, the counting value cnt (n) at the moment is recorded in the FPGA;

step four, when the button is pressed to release the small ball, the counter in the FPGA starts counting, when the small ball passes through the first pair of laser pair tubes, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the first pair of laser pair tubes is recorded as cnt0, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the second pair of laser pair tubes is recorded as cnt1, and so on, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the nth pair of laser pair tubes is recorded as cnt (n-1);

step five, recording the time from the rising edge of the first pair of laser pair tubes to the rising edge of the second pair of laser pair tubes as t₁Time t₁The count cnt1 counted from the time the counter is pressed by the key until the ball falls on the second pair of laser pair transistors to generate a rising edge is subtracted from the count cnt0 counted from the time the counter is pressed by the key until the ball falls on the first pair of laser pair transistors to generate a rising edge is multiplied by the clock sampling period T_clk(ii) a And by analogy, the count cnt (n-1) counted from the time when the counter is pressed down to the time when the ball falls to the nth pair of laser pair tubes to generate the rising edge is subtracted from the count cnt0 counted from the time when the counter is pressed down to the time when the ball falls to the first pair of laser pair tubes to generate the rising edge, and the result is multiplied by the clock sampling period T_clkIs denoted by t_nThe time from the first pair of laser pair tubes to the Nth pair of laser pair tubes of the small ball is expressed as t₁、t₂、...、t_nRecording in sequence;

recording the precise coordinates of the first pair of laser pair tubes as x₁The precise coordinates of the second pair of laser pair tubes are denoted as x₂And recording the accurate coordinate of the Nth pair of laser pair tubes as x_N(ii) a Precise coordinates x of the second pair of laser pair tubes₁Subtract the exact coordinates x of the first pair of laser pairs₂Is marked as S₁Precise coordinates x of a third pair of laser pair tubes₃Subtract the exact coordinates x of the first pair of laser pairs₁Is marked as S₂And by analogy, the accurate coordinate x of the Nth pair of laser pair tubes_NSubtract the exact coordinates x of the first pair of laser pairs₁Is marked as S_N；

And seventhly, after the measurement and the recording are finished, the time and the displacement of the two pairs of laser geminate transistors correspond to each other, and the NiosII soft core CPU embedded in the FPGA processes the acquired time and displacement and then displays the gravity acceleration g value on the LCD.

2. The FPGA-based laser tube gravity detection method of claim 1, wherein the specific process of calculating the gravitational acceleration by the CPU in the seventh step according to the acquired time and displacement data by using a least square method is as follows: by the pellet equation of state:

g is the gravitational acceleration value of the point; the displacement of the ball in the vacuum system is s_n(N ═ 1,2, …, N); taking the frequency of a high-speed clock inside the FPGA as a reference, and measuring the time corresponding to the falling displacement of the small ball to be t_n(N ═ 1,2, …, N); and substituting the displacement measured by a plurality of positions and time into a state equation to obtain:

moving the right term of the equation to the left, summing the squares of the right term of the equation to form an overdetermined equation set with the measurement result, and converting the problem of solving the g value into least square to search s_nAnd t_nFunction matching:

the function matching is converted into equation form by partial derivative:

to obtain information about g and v₀The set of equations of:

the above formula matrix is abbreviated as AX ═ B;

X＝A^-1B；

x is a least squares solution of the set of equations to find s_nAnd t_nIs matched with the optimal function to obtain the gravity acceleration of the point

3. An FPGA-based laser pair tube gravity detector for implementing the FPGA-based laser pair tube gravity detection method according to any one of claims 1 to 2, wherein the FPGA-based laser pair tube gravity detector is provided with a container;

the container is provided with FPGA and power, and FPGA is connected with electric pressure sensor, LCD display screen, Wifi module, button and receiver electricity.

4. The FPGA-based laser geminate transistor gravity detector as claimed in claim 3, wherein the FPGA is electrically connected with an electromagnetic relay, the electromagnetic relay is electrically connected with an electromagnet, and a small ball is placed at the lower end of the electromagnet.

5. The FPGA-based laser geminate gravity detector of claim 3, wherein the power supply is connected with the FPGA, the electromagnetic relay, the electromagnet and the emitter through wires.

Technical Field

The invention belongs to the technical field of gravity detection, and particularly relates to a laser pair tube gravity detector and a detection method based on an FPGA.

Background

The gravity field is a geophysical basic field reflecting the internal material structure and the change of the internal material structure of the earth, and the high-precision absolute gravity observation data is the basis of the research in the fields of seismic monitoring and forecasting, geoscience research, resource exploration and the like. Although many countries have developed international exploration on absolute gravity observation technology, only two types of absolute gravimeters, namely FG5 and A10, produced by American Micro-G company are practically used, and export control is implemented in China, so that the price is high, and the maintenance period is long. Although the experts of the Chinese measurement science research institute introduced two types of NIM-I and N I M-II absolute gravimeters with the same international measurement precision level in the seventy-eight years of the twentieth century, the method only stays in the experimental prototype stage and cannot form products. Meanwhile, with the rapid development of China in the fields of time reference, length reference, high-precision digital acquisition and control, broadband high-precision vibration measurement technology and the like in recent years, the research of the high-precision absolute gravimeter with independent intellectual property rights becomes possible.

The existing gravity detector has the following measurement process: firstly, the data processing and control system sends an instruction, the motor rotates forwards, and the vacuum bin and the falling object are driven by the transmission device to slowly rise to the top of the vacuum falling system; then the motor rotates reversely, and the vacuum bin falls at an acceleration slightly larger than g; the falling object is separated from the vacuum bin to realize free falling; the frequency of the interference fringes is increased along with the increase of the speed of the falling object, when the frequency of the interference fringes reaches a set value, the high-speed signal acquisition system starts to sample output signals of the laser interference system and the vacuum bin displacement measurement system, and the sampling is stopped when the data volume meets the requirement of subsequent calculation; the acceleration of the vacuum bin is reduced in the final stage of falling, and the motor decelerates until the falling object is stopped after the falling object is in contact with the vacuum bin again; meanwhile, an air refractive index measuring system measures the air refractive index on the path of the measuring arm of the laser interferometer; and the data processing and control system acquires the data of the measuring system, and the software fits and calculates the g value and displays the g value. The gravity detector can realize continuous measurement by repeating the above processes.

Through the above analysis, the problems and defects of the prior art are as follows:

(1) in the prior art, a vacuum bin displacement measuring system and a laser interference measuring system are subjected to signal acquisition, the sampling frequency of a reference clock is only 10MHz, and high-speed signals cannot be effectively acquired, so that the measurement accuracy of the gravity acceleration is not very accurate.

(2) The existing gravity detector is large in size, high in price and not suitable for civil outdoor exploration.

The difficulty in solving the above problems and defects is: how to manufacture a high-precision gravity acceleration detector, and the detector is low in price and convenient to carry out exploration.

The significance of solving the problems and the defects is as follows: the self-made high-precision gravity detector can be applied to the aspect of ore exploration, solves the problem that China is imported in other countries, meets the user requirements of domestic related fields, and also solves the problems of maintenance and forbidden transportation. And the self-made high-precision gravity detector is small and exquisite, has a light machine body, is convenient for field exploration, and is a breakthrough in China.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a laser pair tube gravity detector based on an FPGA and a detection method. The method accurately measures the free falling time of the metal pellets by using a plurality of laser geminate transistors in a container which is pumped to be close to vacuum, and then calculates the gravity acceleration by using least square fitting in combination with coordinate values of the geminate transistors.

The invention is realized in such a way that a laser geminate transistor gravity detection method based on FPGA conveniently comprises the following steps:

firstly, pumping air in a container completely by using a vacuum pump, so that the movement of the small ball is not influenced by air resistance, and the small ball does free-falling body movement; in the air extraction process, the pressure sensor controlled by the FPGA can acquire the pressure in the system and display the pressure on the LCD screen, and the vacuum pump is controlled;

after the interior of the container becomes vacuum, the electromagnetic relay is controlled to release the small balls through connection of a mobile phone APP developed by the user and a WiFi module of the FPGA, or the electromagnetic relay is controlled to release the small balls directly through keys on the FPGA;

step three, when the FPGA receives a control instruction of a mobile phone or a key, the FPGA immediately controls an electromagnetic relay to release a small ball, when the small ball falls down to the laser geminate transistor, the CPU immediately starts a high-speed clock in the FPGA, and when the clock is triggered, a series of pulse sequence counts can be generated;

and step four, when the key is pressed to release the small ball, the counter in the FPGA starts counting, when the small ball passes through the first pair of laser pair tubes, the number of rising edges generated by the counter from the time when the key is pressed to the time when the small ball falls to the first pair of laser pair tubes is recorded as cnt0, the number of rising edges generated by the counter from the time when the key is pressed to the time when the small ball falls to the second pair of laser pair tubes is recorded as cnt1, and so on, and the number of rising edges generated by the counter from the time when the key is pressed to the time when the small ball falls to the nth pair of laser pair tubes is recorded as cnt (n-1).

Step five, recording the time from the rising edge of the first pair of laser pair tubes to the rising edge of the second pair of laser pair tubes as t₁Time t₁The count cnt1 counted from the time the counter is pressed by the key until the ball falls on the second pair of laser pair transistors to generate a rising edge is subtracted from the count cnt0 counted from the time the counter is pressed by the key until the ball falls on the first pair of laser pair transistors to generate a rising edge is multiplied by the clock sampling period T_clk. And by analogy, the count cnt (n-1) counted from the time when the counter is pressed down to the time when the ball falls to the nth pair of laser pair tubes to generate the rising edge is subtracted from the count cnt0 counted from the time when the counter is pressed down to the time when the ball falls to the first pair of laser pair tubes to generate the rising edge, and the result is multiplied by the clock sampling period T_clkIs denoted by t_nThe time from the first pair of laser pair tubes to the Nth pair of laser pair tubes of the small ball is expressed as t₁、t₂、...、t_nRecording in sequence;

recording the precise coordinates of the first pair of laser pair tubes as x₁The precise coordinates of the second pair of laser pair tubes are denoted as x₂And recording the accurate coordinate of the Nth pair of laser pair tubes as x_N. Precise coordinates x of the second pair of laser pair tubes₁Subtract the exact coordinates x of the first pair of laser pairs₂Is marked as S₁Precise coordinates x of a third pair of laser pair tubes₃Minus the first pair of lasersExact coordinates x of the tubes₁Is marked as S₂And by analogy, the accurate coordinate x of the Nth pair of laser pair tubes_NSubtract the exact coordinates x of the first pair of laser pairs₁Is marked as S_N；

And seventhly, after the measurement and the recording are finished, the time and the displacement of the two pairs of laser geminate transistors correspond to each other, and the NiosII soft core CPU embedded in the FPGA processes the acquired time and displacement and then displays the gravity acceleration g value on the LCD.

Further, in the seventh step, the specific process of calculating the gravitational acceleration by the CPU according to the collected time and displacement data by using a least square method is as follows:

n pairs of laser geminate transistors are arranged on the FPGA-based laser geminate transistor gravity detector, the small ball is supposed to make free falling body motion in a uniform gravity field, the gravity acceleration value of the field is the gravity acceleration value of a certain point below the falling starting point of the real gravity field, the point is taken as an observation point, the distance from the initial position of the small ball to the point is called as an effective height, and the distance from the point to the beginning and end positions of the falling small ball is called as a reference height; an equation of state can be instantiated by the state of the ball passing through this point

g is the gravitational acceleration value of the point;

the laser wavelength of a laser geminate transistor gravity detector based on FPGA is taken as a reference, and the displacement of the small ball doing free-falling body motion in a vacuum system is s_n(N ═ 1,2, …, N); taking the frequency of a high-speed clock inside the FPGA as a reference, and measuring the time corresponding to the falling displacement of the small ball to be t_n(N ═ 1,2, …, N); substituting the measured displacements at multiple positions with time into equation of state (1) yields:

moving the right term of the equation to the left and summing the squares thereof so that the equation of state and the measurement result form an overdetermined system of equations, and therefore solving for the g valueQuestion conversion to least squares finding s_nAnd t_nAnd (3) matching an optimal function:

the optimum function matching is converted into equation form by partial derivative

The reduction of (4) leads to the reduction of g and v₀The set of equations of:

the above matrix is abbreviated as AX ═ B (6)

X＝A^-1B (7)

X is a least squares solution of the set of equations to find s_nAnd t_nIs matched with the best function, i.e. the gravitational acceleration at that point is foundThe optimum value of (2).

The invention also aims to provide the FPGA-based laser geminate transistor gravity detector for implementing the detection method of the FPGA-based laser geminate transistor gravity detector, the FPGA-based laser geminate transistor gravity detector is provided with a container, the container is provided with an FPGA and a power supply, and the FPGA is electrically connected with an electric pressure sensor, an LCD display screen, a Wifi module, a key and a receiver.

Furthermore, FPGA is connected with first electromagnetic relay electricity, and electromagnetic relay is connected with the electro-magnet electricity, and the bobble has been placed to the electro-magnet lower extreme.

Furthermore, the power supply is connected with the FPGA, the electromagnetic relay, the electromagnet and the emitter through leads.

In summary, the advantages and positive effects of the invention are: according to the invention, a clock with the frequency of 200MHz generated by a constant-temperature crystal oscillator in the FPGA is used for accurately detecting the triggering time of the laser geminate transistor, so that the time measurement precision can reach 5 nanoseconds; the gravity acceleration is calculated by adopting a least square method, and the algorithm is insensitive to the initial speed and position of the small ball and the reaction time of the electromagnetic relay, so that the measurement precision is improved. Meanwhile, the system precision is analyzed by combining the sampling frequency of the FPGA with a set equation set, which is favorable for explaining that the measurement precision is closely related to the number of laser pair tubes, and the analysis method is proved to be correct; the container is evacuated to reduce the effect of air resistance and the effect of residual air is further eliminated by modeling the density of residual air in the container on the gravity measurements.

In conclusion, the invention fully combines the FPGA intelligent control technology, the laser detection technology and the vacuum technology, uses least square fitting to obtain the gravity acceleration g, and analyzes the system precision, so that the whole system has the characteristics of high precision, simple operation, high cost performance and the like.

Drawings

Fig. 1 is a schematic structural diagram of a laser-to-tube gravity detector based on an FPGA according to an embodiment of the present invention.

In the figure: 1. a container; 2. a power source; 3. an air pressure sensor; 4. an FPGA; 5. an LCD display screen; 6. a Wifi module; 7. pressing a key; 8. an electromagnetic relay; 9. an electromagnet; 10. a transmitter; 11. a receiver.

Fig. 2 is a flowchart of a detection method of a laser pair tube gravity detector based on an FPGA according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of a relationship between a laser pair tube logarithm and measurement accuracy, which can be obtained by using Matlab simulation according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Aiming at the problems in the prior art, the invention provides a laser pair tube gravity detector based on an FPGA and a detection method thereof, and the invention is described in detail with reference to the accompanying drawings.

As shown in fig. 1, the laser pair tube gravity detector based on the FPGA provided in the embodiment of the present invention includes: the device comprises a container 1, a power supply 2, an air pressure sensor 3, an FPGA4, an LCD display screen 5, a Wifi module 6, a key 7, an electromagnetic relay 8, an electromagnet 9, a transmitter 10 and a receiver 11.

The container 1 is provided with an FPGA4 and a power supply 2, and the FPGA4 is electrically connected with the electric pressure sensor 3, the LCD display screen 5, the Wifi module 6, the key 7 and the receiver 11.

The power supply 2 is connected with the FPGA4, the electromagnetic relay 8, the electromagnet 9 and the emitter 10 through leads.

FPGA4 is connected with electromagnetic relay 8 electricity, and electromagnetic relay 8 is connected with electro-magnet 9 electricity, and the pellet has been placed to electro-magnet 9 lower extreme.

As shown in fig. 2, the method for detecting a gravity detector of a pair of laser tubes based on an FPGA according to an embodiment of the present invention includes:

s101: the vacuum pump is utilized to completely pump the air in the container, so that the movement of the small ball is not influenced by air resistance, and the small ball does free-falling body movement; in the air extraction process, the pressure sensor controlled by the FPGA can acquire the pressure in the system and display the pressure on the LCD screen, and the vacuum pump is controlled;

s102: after the interior of the container becomes vacuum, the electromagnetic relay is controlled to release the small balls through connection of a mobile phone APP developed by the user and a WiFi module of the FPGA, or the electromagnetic relay is controlled to release the small balls directly through keys on the FPGA;

s103: when the FPGA receives a control instruction of a mobile phone or a key, the FPGA immediately controls the electromagnetic relay to release the small ball, when the small ball falls to the laser geminate transistor, the CPU immediately starts a high-speed clock in the FPGA, and the clock generates a series of pulse sequence counting when being triggered;

s104: when the ball passes through the first pair of laser pair tubes, the counter c1 starts counting from the first rising edge of the pulse sequence, the counter c1 does not end until the ball triggers the second pair of laser pair tubes to generate a rising edge, and c2 starts counting again when c1 ends; in a cycle, the small ball is finished through an Nth pair of laser pipe timing counter c (N-1);

s105: the falling time of the small ball passing through two points is measured by multiplying the number of rising edge clock counters of the two pulse sequences by the clock sampling period, and the time of the small ball from the first pair of laser pair tubes to the Nth pair of laser pair tubes is recorded in sequence;

s106: recording the distance between the first pair of laser pair tubes and the second pair of laser pair tubes, recording the distance between the second pair and the third pair, and so on, and recording the distance between the (N-1) th pair of laser pair tubes and the Nth pair of laser pair tubes;

s107: after the measurement and recording are finished, the time and the displacement of the two pairs of laser geminate transistors correspond to the time and the displacement of the two pairs of laser geminate transistors, and the NiosII soft core CPU embedded in the FPGA processes the acquired time and displacement and then displays the gravity acceleration value on the LCD.

The detection method of the laser geminate transistor gravity detector based on the FPGA provided by the embodiment of the invention specifically comprises the following steps:

firstly, pumping air in a container completely by using a vacuum pump, so that the movement of the small balls is not influenced by air resistance, and the small balls do free-falling body movement; in the air extraction process, the pressure sensor controlled by the FPGA can acquire the pressure in the system and display the pressure on the LCD screen, and the vacuum pump is controlled.

And secondly, after the inside of the container becomes vacuum, the electromagnetic relay is controlled to release the small balls through the connection of the mobile phone APP developed by the user and the WiFi module of the FPGA, or the electromagnetic relay is controlled to release the small balls directly through keys on the FPGA.

And thirdly, when the FPGA receives a control instruction of the mobile phone or the key, the FPGA immediately controls the electromagnetic relay to release the small ball, when the small ball falls down to the laser geminate transistor, the CPU immediately starts a high-speed clock in the FPGA, and when the clock is triggered, a series of pulse sequence counting can be generated.

Fourthly, when the button is pressed to release the small ball, the counter in the FPGA starts to count, when the small ball passes through the first pair of laser pair tubes, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the first pair of laser pair tubes is recorded as cnt0, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the second pair of laser pair tubes is recorded as cnt1, and so on, and the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the nth pair of laser pair tubes is recorded as cnt (n-1).

Fifthly, the falling time t of the small ball passing through two points is measured by multiplying the number of rising edge clock counters of the two pulse sequences by the clock sampling period, and the time from the first pair of laser pair tubes to the Nth pair of laser pair tubes of the small ball is measured according to t₁、t₂、...、t_nAnd recording the results in turn.

Sixthly, recording the time from the rising edge of the first pair of laser pair tubes to the rising edge of the second pair of laser pair tubes as t₁Time t₁The count cnt1 counted from the time the counter is pressed by the key until the ball falls on the second pair of laser pair transistors to generate a rising edge is subtracted from the count cnt0 counted from the time the counter is pressed by the key until the ball falls on the first pair of laser pair transistors to generate a rising edge is multiplied by the clock sampling period T_clk. And by analogy, the count cnt (n-1) counted from the time when the counter is pressed down to the time when the ball falls to the nth pair of laser pair tubes to generate the rising edge is subtracted from the count cnt0 counted from the time when the counter is pressed down to the time when the ball falls to the first pair of laser pair tubes to generate the rising edge, and the result is multiplied by the clock sampling period T_clkIs denoted by t_nThe time from the first pair of laser pair tubes to the Nth pair of laser pair tubes of the small ball is expressed as t₁、t₂、...、t_nRecording in sequence;

seventhly, recording the accurate coordinates of the first pair of laser pair tubes as x₁The precise coordinates of the second pair of laser pair tubes are denoted as x₂And recording the accurate coordinate of the Nth pair of laser pair tubes as x_N. Precise coordinates x of the second pair of laser pair tubes₁Subtract the exact coordinates x of the first pair of laser pairs₂Is marked as S₁Precise coordinates x of a third pair of laser pair tubes₃Subtract the exact coordinates x of the first pair of laser pairs₁Is marked as S₂And by analogy, the accurate coordinate x of the Nth pair of laser pair tubes_NSubtract the exact coordinates x of the first pair of laser pairs₁Is marked as S_N；

In the sixth step, the specific process of calculating the gravitational acceleration by the CPU according to the collected time and displacement data by using the least square method is as follows:

n pairs of laser geminate transistors are arranged on the FPGA-based laser geminate transistor gravity detector, the small ball is supposed to make free falling body motion in a uniform gravity field, the gravity acceleration value of the field is the gravity acceleration value of a certain point below the falling starting point of the real gravity field, the point is taken as an observation point, the distance from the initial position of the small ball to the point is called as an effective height, and the distance from the point to the beginning and end positions of the falling small ball is called as a reference height; an equation of state can be instantiated from the state of the ball passing through this point:

g is the gravitational acceleration value of the point;

the laser wavelength of a laser geminate transistor gravity detector based on FPGA is taken as a reference, and the displacement of the small ball doing free-falling body motion in a vacuum system is s_n(N ═ 1,2, …, N); taking the frequency of a high-speed clock inside the FPGA as a reference, and measuring the time corresponding to the falling displacement of the small ball to be t_n(N ═ 1,2, …, N); substituting the measured displacements at multiple positions with time into equation of state (1) yields:

moving the right term of the equation to the left, and summing the squares of the right term of the equation to form an overdetermined equation set with the measurement result, thereby converting the problem of solving the g value into least square searching s_nAnd t_nAnd (3) matching an optimal function:

the optimum function matching is converted into equation form by partial derivative

The reduction of (4) leads to the reduction of g and v₀The set of equations of:

the above matrix is abbreviated as AX ═ B (6)

X＝A^-1B (7)

X is a least squares solution of the set of equations to find s_nAnd t_nIs matched with the best function, i.e. the gravitational acceleration at that point is foundThe optimum value of (2).

The technical effects of the present invention will be further described with reference to simulation experiments.

According to the system precision analysis of the invention, the laser tube is packaged by using the II-type structure sealing box, and the laser tube can be stably and firmly fixed on the sealing box by adopting the II-type structure packaging. And then the laser geminate transistors are sequentially placed in the FPGA-based laser geminate transistor gravity detector according to a fixed distance through accurate coordinates, so that the transmitting port and the receiving port are ensured to be positioned on the same horizontal line, no displacement measurement error is generated when the laser transmitting port is shielded by the falling of a small ball, and the function is to reduce system errors and improve measurement accuracy. The gravity acceleration g is represented by time t and displacement S:

let the acceleration g of the weight be equivalent to a function f related to the time displacement, i.e.

(2)。

Taking the derivative of the gravity acceleration g to obtain a relation formula related to displacement and time:

and (4) carrying out chemical solution on the (3) to obtain:

the laser pair tubes are sequentially arranged at a fixed distance through accurate coordinate values, and due to the resistance reduction effect of the vacuum system, the electromagnetic relay releases small balls without resistance to free falling body movement, and the movement track of the electromagnetic relay is a straight line perpendicular to the laser at one half of the position. When the measured distance is equal to the actual drop displacement, the introduced displacement measurement error is zero, i.e. the measurement error is zeroTherefore, it is not only easy to use

(5)。

Clock sampling period based on 200MHz clock frequency

Sampling period T of clock_CDerivation of a derivative(6)。

Let the clock counter number (N _ T)_C) How many clock sampling periods (T) a pellet goes through_C) The clock sampling period (T) of the ball received by each laser pair tube, namely 2 nd, 3 rd, … th laser pair tube_C) Number, the clock counter number (N _ T) of FPGA_C) Multiplied by the clock sample period (T)_C) Obtaining the moment T of triggering the laser pair tube by the small ball as N _ T_C×T_CAnd subtracting the time of the (N-1) pair of laser pair tubes from the time of the Nth pair of laser pair tubes to obtain the falling time of the distance. To (6) is simplified to obtainNamely, it isAndequivalence, therefore, derive

Suppose that a given gravitational acceleration g is 9.8m/s²The vertical falling distance of the small ball is 1m, the initial position of the first pair of laser pair tubes is 0.2cm, and the number of the FPGA passing through the clock counter is (N _ T)_C) Multiplied by the clock period (T)_C) The time t for the ball to freely fall from the electromagnetic relay to the first pair of laser pair tubes can be calculated₀I.e. the moment when the first pair of laser pair tubes is reached, using v₀＝gt₀The initial velocity of the pellet through the first pair of laser pairs is determined. Substituting the corresponding time difference t and falling displacement s of the two laser pair tubes into a set equation system of a second section (5) formula to obtain a new gravity acceleration g _ get valueThe measurement accuracy of the gravity acceleration can be obtained, and different measurement accuracies can be obtained by different laser tube counts. The relationship between the laser pair tube logarithm and the measurement accuracy can be obtained by utilizing Matlab simulation, as shown in FIG. 3, and a curve with the measurement accuracy increasing with the increase of the laser pair tube logarithm is obtained by performing linear fitting on the relationship.

Therefore, when the small ball which is in free fall in the vacuum system passes through the laser pair pipe which is placed in accurate coordinates, no displacement measurement error is introduced, and the measurement accuracy of the system is only closely related to the measurement accuracy of time. The more laser geminate transistors are arranged, the higher the measurement precision of the falling time of the small ball is, the smaller the system error is, the stronger the system performance is, and the measured gravity acceleration value is closer to a theoretical value.

The working principle of the invention is as follows: the vacuum pump is utilized to completely pump the air in the container, so that the movement of the small ball is not influenced by air resistance, and the small ball does free-falling body movement; in the air extraction process, the pressure sensor controlled by the FPGA can acquire the pressure in the system and display the pressure on the LCD screen, and the vacuum pump is controlled. After the inside of the container becomes vacuum, the mobile phone APP developed by the user is connected with the WiFi module of the FPGA to control the electromagnetic relay to release the small ball, or the electromagnetic relay is directly controlled by the keys on the FPGA to release the small ball.

When the FPGA receives a control instruction of a mobile phone or a key, the FPGA immediately controls the electromagnetic relay to release the small ball, when the small ball falls to the laser geminate transistor, the CPU immediately starts a high-speed clock in the FPGA, and the clock generates a series of pulse sequence counting when being triggered. When the button is pressed to release the small ball, the counter in the FPGA starts to count, when the small ball passes through the first pair of laser pair tubes, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the first pair of laser pair tubes is recorded as cnt0, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the second pair of laser pair tubes is recorded as cnt1, and so on, the number of rising edges generated by the counter from the time when the button is pressed to the time when the small ball falls to the nth pair of laser pair tubes is recorded as cnt (n-1).

Recording the time from the rising edge of the first pair of laser pair tubes to the rising edge of the second pair of laser pair tubes as t₁Time t₁The count cnt1 counted from the time the counter is pressed by the key until the ball falls on the second pair of laser pair transistors to generate a rising edge is subtracted from the count cnt0 counted from the time the counter is pressed by the key until the ball falls on the first pair of laser pair transistors to generate a rising edge is multiplied by the clock sampling period T_clk. And by analogy, the count cnt (n-1) counted from the time when the counter is pressed down to the time when the ball falls to the nth pair of laser pair tubes to generate the rising edge is subtracted from the count cnt0 counted from the time when the counter is pressed down to the time when the ball falls to the first pair of laser pair tubes to generate the rising edge, and the result is multiplied by the clock sampling period T_clkIs denoted by t_nThe time from the first pair of laser pair tubes to the Nth pair of laser pair tubes of the small ball is expressed as t₁、t₂、...、t_nRecording in sequence;

the precise coordinates of the first pair of laser pair tubes are denoted as x₁The precise coordinates of the second pair of laser pair tubes are denoted as x₂Will beThe precise coordinate of the Nth pair of laser pair tubes is recorded as x_N. Precise coordinates x of the second pair of laser pair tubes₁Subtract the exact coordinates x of the first pair of laser pairs₂Is marked as S₁Precise coordinates x of a third pair of laser pair tubes₃Subtract the exact coordinates x of the first pair of laser pairs₁Is marked as S₂And by analogy, the accurate coordinate x of the Nth pair of laser pair tubes_NSubtract the exact coordinates x of the first pair of laser pairs₁Is marked as S_N；

After the measurement and recording are finished, the time and the displacement of the two pairs of laser geminate transistors correspond to the time and the displacement of the two pairs of laser geminate transistors, and the NiosII soft core CPU embedded in the FPGA processes the acquired time and displacement and then displays the gravity acceleration g value on the LCD.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.