JP5099424B2 - Gravity gradient measuring device - Google Patents

Description

  The present invention relates to a gravity gradient measuring apparatus, and preferably relates to a gravity gradient measuring apparatus used by being mounted on a moving body.

  FG5 absolute gravitational accelerometer and LaCoste Romberg gravimeter are known as devices capable of measuring gravitational acceleration with a sensitivity of 1 micro Gal in measuring gravitational acceleration. The FG5 absolute gravitational accelerometer (Patent Document 1) measures the absolute acceleration of a fallen body due to free fall with μGal accuracy. The La-Coste Romberg gravimeter measures relative gravitational acceleration with an accuracy of 1μGal and is mainly used for field work. Both have been applied to resource exploration and geophysical research, but if you are on a moving body such as an airship to survey a wide area in a short time, the correct measurement value will not be obtained unless the acceleration of the moving body is subtracted. do not become. However, knowing the acceleration of the moving body at the 1 micro Gal level means that the position measurement accuracy is increased to 8 digits by GPS or laser distance measurement technology with the ground, which is impossible in reality.

  Therefore, focusing on the fact that the gravitational acceleration value required for resource exploration etc. is not an absolute value but a change (gradient) in gravitational acceleration, the gravitational acceleration gradient is precisely measured in a form in which the motion of the airship does not affect the measurement. I thought to measure. The principle of gravitational gradient measurement is to make an object corresponding to two mirrors of a Michelson interferometer freely fall separately and measure the temporal change in displacement between them by the output of the interferometer. Gravity gradient measurement adopts the measurement principle that the earth's gravity is canceled and takes out only the change of gravity due to local mass distribution. Thanks to this ingenuity, even if the measuring instrument itself is accelerating, the acceleration is not reflected in the measured value, and therefore is not affected by the acceleration of the moving object.

  Some proposals have already been made on the gravity gradient meter (Patent Documents 2 to 6). These disclose the basic idea of measuring the gradient of gravitational acceleration, but there are problems in terms of limiting the number of repetitions of measurement and accuracy when considering practical use. In fact, this kind of gravimeter has not been put into practical use for many years, even though its idea was shown long ago. That is, improvement in the number of repetitions of measurement in the gravity gradient meter and improvement in measurement accuracy are problems that have not been solved for many years.

It is also possible to measure the gravitational gradient using two FG5 absolute gravitational accelerometers with sufficient measurement accuracy, but in this case, the acceleration of the reference reflector that is the basis of gravitational acceleration is assumed. The identity is not compensated, and there is a risk that a system error may occur, and the entire apparatus becomes larger and the cost increases.
US Pat. No. 5,351,122 JP 47-18578 U.S. Pat. No. 3,688,584 US Pat. No. 3,693,451 U.S. Pat. No. 3,704,626 U.S. Pat. No. 3,727,462

  The present invention aims to solve the above-mentioned problems.

In order to solve such a problem, the gravity gradient measuring device adopted by the present invention is:
A first free-falling body comprising a first reflecting mirror;
A second free-falling body provided with a second reflecting mirror;
A first suspension mechanism comprising: a fixed portion; and a movable portion movable up and down between an upper position and a lower position with respect to the fixed portion, and a first free-falling body suspended from the movable portion. ,
A second suspension mechanism comprising: a fixed portion; and a movable portion that can move up and down between an upper position and a lower position relative to the fixed portion, and a second free-falling body is suspended from the movable portion. ,
A first release mechanism for releasing the first free-falling body from the movable part of the first suspension mechanism in the upper position;
A second release mechanism for releasing the second free-falling body from the movable part of the second suspension mechanism in the upper position;
A mechanism for moving the movable part of the first suspension mechanism up and down, wherein when the first free-falling body is released, the movable part is moved down with an acceleration larger than the free fall of the first free-falling body, and the first free-falling body A first support mechanism configured to move the movable part at the lower position to the upper position together with the first free faller suspended by the movable part after the free fall;
A mechanism for moving the movable part of the second suspension mechanism up and down, wherein when the second free-falling body is released, the movable part is moved down with an acceleration larger than the free fall of the second free-falling body, and the second free-falling body A second support mechanism configured to move the movable part at the lower position to the upper position together with the second free-falling body suspended by the movable part after the free fall;
At least a casing for accommodating the first free fall body and the second free fall body in a vacuum state;
A light source;
When the first free-falling body and the second free-falling body are free-falling, the light beam emitted from the light source is directed to the first reflecting mirror and the second reflecting mirror, respectively. An optical system constituting a Michelson interferometer that generates interference of both reflected light beams from two reflecting mirrors;
A photodetector for receiving the interference light generated by the optical system;
Means for obtaining a gravitational gradient from the interference light received by the photodetector;
Consists of.

  In one preferable aspect, the first free fall body further includes a beam splitter, and the first free fall body and the second free fall body have the beam splitter emit a light beam emitted from a light source. The beams are directed to the first reflecting mirror and the second reflecting mirror, respectively, so that the beam splitter receives the reflected light beams from the first reflecting mirror and the second reflecting mirror and generates interference between the reflected light beams. It is installed.

  In one preferable aspect, each of the first release mechanism and the second release mechanism includes a piezoelectric element provided in each movable portion, and each piezoelectric element is extended in response to voltage application to each free fall body. Each free-falling body is configured to be released from the movable portion of each suspension mechanism by instantaneously expanding and contracting after moving up.

  In one aspect, the piezoelectric element is provided in a support portion where each movable portion supports each free-falling body. In a more specific embodiment, each movable part is a quadrilateral frame, and the support part is formed on a horizontal lower frame of the quadrilateral frame.

  In one aspect, the piezoelectric element is arranged so as to extend each movable part upward at each movable part, and is suspended from each movable part by extending the piezoelectric element. Each free fall body is configured to move up. In a more specific mode example, each movable part is a quadrilateral frame, and the piezoelectric elements are provided on the left and right side frames of the quadruple frame.

  In one aspect, each free fall body is suspended from each movable part by point contact. In a more specific example, a small sphere is provided at the upper end of the support portion of the movable portion, and the free fall body is supported via the small sphere. Alternatively, a small ball may be provided on each free-falling body side, and a small ball receiving portion may be formed at the upper end of the support portion of the movable portion.

In one embodiment, each support mechanism is
Means for urging each movable part in the upper position toward the lower side;
A locking means that is detachable with respect to each movable part in the upper position, and holds the movable part in the upper position;
Means for moving each movable part from the lower position to the upper position;
It has.
In a more specific embodiment, the upward movement means includes a lifting bar connected to each movable portion and a driving means for moving the lifting bar upward. A motor is typically exemplified as a drive source of the drive means, and it is configured so that the lifting rod can be moved up and down by transmitting the rotational force of the motor to the vertical movement of the lifting rod through the transmission means. Examples of the transmission means include those using a cam and those using a gear.

  In one aspect, the said 1st free fall body and the said 2nd free fall body are arrange | positioned at intervals in the perpendicular direction, and it is comprised so that a vertical gravity gradient may be measured.

  In one aspect, the said 1st free fall body and the said 2nd free fall body are arrange | positioned at intervals in the horizontal direction, and are comprised so that a horizontal gravity gradient may be measured.

In one embodiment,
In the falling body main body of the first free-falling body, two accommodating portions for accommodating the first reflecting mirror so as to be freely inserted and removed are formed,
When the first reflecting mirror is located in the first housing part, it reflects the light beam from the first direction,
When the first reflecting mirror is positioned in the second housing portion, the light beam from the second direction orthogonal to the first direction is reflected.
By doing so, it is possible to form a free fall body that is used for both vertical gravity gradient measurement and horizontal gravity gradient measurement.

In one embodiment,
The falling body body of the second free-falling body is provided with a first hanging portion and a second hanging portion that extend in directions orthogonal to each other,
Each of the first suspension part and the second suspension part is detachable from the movable part,
When the second free fall body is suspended from the movable part via the first suspension part, the second reflecting mirror reflects the light beam from the first direction,
When the second free fall body is suspended from the movable part via the second suspension part, the second reflecting mirror reflects the light beam from the second direction orthogonal to the first direction. .
The structure which makes the 1st suspension part and the 2nd suspension part detachable with respect to a movable part makes disassembly of one or both of these suspension parts and a movable part, or a part rotatable. Is possible.
By doing so, it is possible to form a free fall body that is used for both vertical gravity gradient measurement and horizontal gravity gradient measurement.

  ADVANTAGE OF THE INVENTION According to this invention, the gravity gradient measuring apparatus which can raise the frequency | count of measurement repetition can be provided. Specifically, the number of repetitions of measurement can be increased by adopting the first support mechanism and the second support mechanism that constitute the drop mechanism and the return mechanism.

  The present invention can improve measurement accuracy while having a simple configuration. Specifically, by mounting the beam splitter on the first free-falling body, it is possible to reduce the number of optical mirrors that are necessary otherwise (as a result, the influence of those mechanical vibrations can be eliminated). ), And the influence of mechanical vibrations of the beam splitter and the necessary mirror occurring within the measurement time can be eliminated. Furthermore, by using a piezoelectric element as a release mechanism for the free fall body, the free fall body can be separated at a high speed so as to reduce the tilt rotation speed. That is, the angular velocity of the falling body, which is an essential requirement for high-accuracy measurement, can be minimized.

  The gravity gradient measuring device measures the relative acceleration between two free-falling bodies that freely move under gravity alone. Hereinafter, a vertical gravity gradient measuring apparatus and a horizontal gravity gradient measuring apparatus according to the present invention will be described with reference to the drawings. In the drawings, the same members are denoted by the same reference numerals. Moreover, the description regarding the member which attached | subjected the same reference number shall mutually be used as needed between a vertical gravity gradient measuring apparatus and a horizontal gravity gradient measuring apparatus.

  A vertical gravity gradient measuring device will be described with reference to FIGS. The vertical gravity gradient measuring device includes a first free fall body 1 and a second free fall body 2. The internal space of the main body casing 3 of the vertical gravity gradient measuring device is divided into an ultrahigh vacuum portion 3A and an atmospheric pressure portion 3B below the ultrahigh vacuum portion 3A via a partition wall 30. A vacuum exhaust device 31 for forming the ultra-high vacuum portion 3 </ b> A is connected to the wall surface of the main casing 3. The first free-falling body 1 and the second free-falling body 2 are arranged in the ultrahigh vacuum part 3A of the main body casing 3 with a space in the vertical direction. In the illustrated embodiment, the first free fall body 1 is disposed on the lower side, and the second free fall body 2 is disposed on the upper side.

  The first free fall body 1 includes a main body 10 and a suspension part 11 formed at the upper end of the main body 10. The main body 10 includes a first reflecting mirror 4A, a beam splitter 5, and a reflecting mirror 6A. The suspension part 11 includes left and right side frames 11a and 11b extending upward from the upper end of the main body 10, and an upper horizontal frame 11c integrally connecting the upper ends of the left and right side frames 11a and 11b. Consists of. The main body 10 is formed with a first housing part 100 (see FIG. 6) and a second housing part 101 into which the first reflecting mirror 4A is removably inserted. In the embodiment shown in FIG. Is inserted into the first housing part 100. The first free fall body 1 is designed such that the center of gravity of the first free fall body 1 and the optical center of the first reflecting mirror 4A coincide. When the first reflecting mirror 4A is a corner cube prism, the optical center is h (1-1 / n) downward from the apex, assuming that the height is h when the height is assumed to be a triangular pyramid with the incident surface as the bottom surface. ) (Where n is the refractive index of the prism material). In the case of glass with a refractive index of 1.5, if the height is 11 mm, the optical center is at a position of about 3.7 mm below the apex. In the case of the first free-falling body 1, it is assumed that the first reflecting mirror (corner cube prism) 4A is in a mirror image position formed by the reflection of the beam splitter 5, and the optical center and the position of the center of gravity are made to coincide. For this reason, the first free fall body 1 is designed so that a high-density substance is concentrated on the upper side so that the entire center of gravity comes to the position. For example, the center of gravity is adjusted by increasing the density and shape of the material of the suspension part 11. When the first reflecting mirror 4A is a corner reflector, the optical center is at its apex.

  The second free-falling body 2 includes a main body 20 and a suspension portion 21 that protrudes from the upper end of the main body 20. The main body 20 includes a second reflecting mirror 4B. Similar to the first free fall body 1, the second free fall body 2 is designed such that the center of gravity of the second free fall body 2 and the optical center of the second reflecting mirror 4B coincide. In the 2nd free fall object 2, an optical center exists in the 2nd reflective mirror (corner cube prism) 4B. The suspension portion 21 includes left and right side frames extending upward from the upper end of the main body 20 and an upper horizontal frame integrally connecting the upper ends of the left and right side frames. In FIG. 1, only one side frame 21a is shown. The main body 20 is further provided with a hanging portion 22 and a protruding portion 23, which will be described later.

  The vertical gravity gradient apparatus is further received by the laser light source 7, an optical system constituting a Michelson interferometer, a photodetector 8 that receives interference fringes generated by the optical system, and the photodetector. Means 9 for obtaining a gravitational gradient from the interference fringes. The interference received by the photodetector 8 is converted into an electrical signal, amplified for later processing by the amplifier 9a, and the electrical gradient is acquired by processing the electrical signal by the power gradient acquisition means 9. The laser light source 7 and the detector 8 are provided in the atmospheric pressure part 3 </ b> B of the main body casing 3. The light beam emitted from the laser light source 7 is introduced into the ultrahigh vacuum portion 3A through the optical window 30a formed in the partition wall 30. In FIG. 1, the laser light source 7 and the light detector 8 are arranged below the free fall bodies 1 and 2. It will be understood by those skilled in the art that it can be installed on the top of the.

  The optical system that constitutes the Michelson interferometer is configured so that the light beams emitted from the laser light source 7 when the first free-falling body 1 and the second free-falling body 2 fall freely are the first reflecting mirror 4A and the second reflecting mirror 4B. Are respectively configured to receive the reflected light beams from the first reflecting mirror 4A and the second reflecting mirror 4B and generate interference between the reflected light beams.

  FIG. 2 is a schematic view showing only the optical system constituting the Michelson interferometer of FIG. The light emitted from the laser light source 7 is directed upward by the reflecting mirror 6B, passes through the optical window 30a formed on the lower wall, and the first light is emitted from the beam splitter 5 (half mirror) provided in the first free fall body 1. The light beam is divided into two light beams, a beam and a second light beam. The first light beam traveling leftward in the horizontal direction is reflected by a reflecting mirror (corner cube prism or corner reflector) 4A provided on the first free fall body 1, and the second light beam traveling upward is second The light is reflected by the reflecting mirror (corner cube prism or corner reflector) 4B of the free-falling body 2. The first light beam reflected by the reflecting mirror 4A and the second light beam reflected by the reflecting mirror 4B are directed to the beam splitter 5 provided in the first free fall body 1, and the reflected first light beam is reflected. The light beams traveling toward the right in the horizontal direction of the reflected second light beams interfere with each other. The interference light is directed downward by the reflecting mirror 6A, and the interference light directed to the lower space (atmospheric pressure part 3B) through the optical window 30b formed in the partition wall 30 is further horizontally directed by the reflecting mirror 6C. The light is directed and received by the photodetector 8. The reflecting mirrors 6A, 6B, and 6C are appropriately installed according to the arrangement of the laser light source 7 and the photodetector 8, and it is easily understood by those skilled in the art that the orientation and arrangement thereof can be changed as appropriate.

  When the two free-falling bodies 1 and 2 fall freely, the distance between the first reflecting mirror, the second reflecting mirror, and the beam splitter (half mirror) 5 is almost constant according to the initial speed of each beam. The relative acceleration is the change that deviates from constant. The value of the relative acceleration is obtained by fitting the interference fringe phase data captured by the photodetector with a quadratic function of time. A method for calculating the relative acceleration from the interference fringes acquired by the interferometer is well known to those skilled in the art, and thus detailed description thereof is omitted. Moreover, acquisition of the gravity gradient from interference is described in Patent Document 2, for example.

  As shown in FIG. 1, a first suspension mechanism 12 and a second suspension mechanism 13 that respectively suspend the first free fall body 1 and the second free fall body 2 are vertically spaced in the casing 3. Exist. In the casing 3, a first support mechanism 14 and a second support mechanism 15 that respectively support the first suspension mechanism 12 and the second suspension mechanism 13 are arranged in the vertical direction with a space therebetween.

  As shown in FIGS. 4 and 5, the first suspension mechanism 12 includes a fixed portion 120 and a movable portion 121 that can move up and down with respect to the fixed portion 120, and the first free fall body 1 includes the movable portion 121. Suspended by. In FIGS. 4 and 5, the first free-falling body 1 is omitted, so please refer to FIGS. 1 and 3 as appropriate. The movable portion 121 is provided on the fixed portion 120 so as to be slidable between an upper position (FIG. 4) and a lower position (FIG. 5). The fixing portion 120 is a frame body that is formed in a gate shape from the left and right side frames 120a and 120b and the upper frame 120c, and whose lower side is open. The fixing portion 120 is supported by the first support mechanism 14 via the upper frame 120c. The movable portion 121 is a quadrilateral frame formed in a vertically long rectangular shape from the left and right side frames 121a and 121b, the upper frame 121c, and the lower frame 121d. In the illustrated example, a horizontal frame 121e is provided at an intermediate portion in the height direction. Guide grooves extending in the vertical direction are formed on the outer sides of the left and right side frames 121a and 121b of the movable portion 121, and are slidable in the vertical direction with respect to the inner sides of the left and right side frames 120a and 120b of the fixed portion 120. It has become.

  A push spring 140 is provided between the upper frame 121c of the movable part 121 and the upper frame 120c of the fixed part 120. The movable part 121 is attached to the fixed part 120 in a direction of moving downward with respect to the fixed part 120. It is energized.

  Claw portions 121f and 121g project from the upper ends of the left and right side frames 121a and 121b of the movable portion 121. On the other hand, the lower ends of spring dampers 120d and 120e extending along the side frames 120a and 120b are fixed to the side frames 120a and 120b of the fixing portion 120. When the movable portion 121 moves downward due to the spring force of the push spring 140 and its own weight, the claw portions 121f and 121g come into contact with the upper ends of the dampers 120d and 120e, respectively, and further downward movement of the movable portion 121 is caused. It is regulated (Fig. 5).

  As shown in FIG. 3, the upper frame 11c of the suspension part 11 of the first free-falling body 1 is supported on the lower frame 121d of the movable part 121 of the first suspension mechanism 12 via the support part 16. With this, the first free fall body 1 is suspended from the movable portion 121. The support portion 16 is provided in a rising shape at the central portion of the length of the lower frame 121 d of the movable portion 121 and includes a piezoelectric element 160. A small ball 161 that supports the upper frame 11c of the suspension portion 11 of the first free-falling body 1 by point contact is provided at the upper end of the support portion 16. Examples of the small sphere 161 include a sapphire sphere, a ruby sphere, a metal sphere, a ceramic sphere, a plastic sphere, and a glass sphere. Balls that are generally used for ball bearings can be used as the small balls 161. The small sphere 161 at the upper end of the support portion 16 is supported by the piezoelectric element 160, and the height position of the small sphere 161 can be changed in the height direction as the piezoelectric element 160 expands and contracts in the vertical direction. . Instead of fixing the small ball 161 to the upper end of the support portion 16, a small ball may be fixed to the lower surface of the lower frame 121 d of the movable portion 121 and a receiving portion may be formed at the upper end of the support portion 16.

  The piezoelectric element 160 provided in the support portion 16 constitutes a first release mechanism that releases the first free fall body 1 from the movable portion 121 of the first suspension mechanism 12. By applying a predetermined voltage to the piezoelectric element 160 by a voltage supply means (not shown), the piezoelectric element 160 is extended upward to move the first free-falling body 1 through the small ball 161, and in this state, When the applied voltage of the piezoelectric element 160 is suddenly reduced to 0 V to instantaneously reduce the piezoelectric element 160, a gap of, for example, about 10 micrometers is formed between the small ball 161 and the first free-falling body 1. The In this way, the first free fall body 1 is released.

  The configuration of the second suspension mechanism 13 is the same as the configuration of the first suspension mechanism 12, and the description of the first suspension mechanism 12 can be applied to the second suspension mechanism 13. The structure of the 2nd release mechanism which releases the 2nd free fall body from the movable part of the 2nd suspension mechanism is also the same, and the above statement can be used.

  The first support mechanism 14 is a mechanism that supports the movable portion 121 of the first suspension mechanism 12 so as to be movable up and down, and from the free fall of the first free fall body 1 when the first free fall body 1 is released. The movable part 121 is moved downward with a large acceleration, and after the first free-falling body 1 is freely dropped, the movable part 121 at the lower position is moved upward together with the first free-falling body 1 suspended by the movable part 121. It is configured to move up to a position.

  The 1st support mechanism 14 is demonstrated based on FIG. 4, FIG. The first support mechanism 14 is detachable with respect to the means for urging the movable part 121 in the upper position toward the lower side and the movable part 121 in the upper position, and holds the movable part 121 in the upper position. Locking means for performing, and means for moving the movable portion 121 from the lower position to the upper position,

  The means for urging the movable portion 121 downward includes the above-described pressing spring 140 provided between the upper frame 121c of the movable portion 121 and the upper frame 120c of the fixed portion 120. When the movable part 121 is in the upper position, a force in the direction of moving the movable part 121 downward acts on the movable part 121 by the spring force of the compressed push spring 140.

  The means for engaging / disengaging the movable part 121 located at the upper position can be engaged / disengaged with the movable part 121 in a state where the movable part 121 is located on the upper side against the spring force by compressing the push spring 140 upward. The rotation locking lever 141 is provided. A locking claw 141a is provided at the tip of the rotation locking lever 141, and a claw portion 121g protruding from the upper end of one (right side) side frame 121a of the movable portion 121 forms a locked portion. Thus, the downward movement of the movable portion 121 is restricted by the locking claw 141a being locked to the claw portion 121g from below (FIG. 4). That is, when the locking claw 141a of the rotation locking lever 141 is locked to the claw portion 121g of the movable portion 121, the movable portion 121 is held at the upper position.

  The rotation locking lever 141 is biased so as to maintain a horizontal posture by a spring means (not shown), and the electromagnetic actuator 142 forcibly rotates the base end side of the rotation locking lever 141 upward. By moving the locking claw 141a on the distal end sideways while rotating downward, the locking claw 141a is disengaged from the locked portion 121g and the locked state is released, and the movable portion 121 is pushed by the push spring 140. It is comprised so that it may move below with the spring force of.

  The means for moving the movable portion 121 upward from the lower position to the upper position includes a pulling rod 143 whose lower end is connected to the upper frame 121c of the movable portion 121, and a drive mechanism for pulling the pulling rod 143 upward. .

  The lower end side of the shaft portion of the lifting rod 143 is inserted through an insertion hole (not shown) formed in the upper frame 121c of the movable portion 121, and the lower end portion of the shaft portion has a larger outer dimension than the insertion hole. It is formed in the formed retaining portion 143a. The lifting rod 143 is also inserted through the upper frame 120 c of the fixed portion 120, and the upper end portion 143 b is connected to a connecting portion 143 c provided at the lower end of the flexible wire 147.

  The drive mechanism is provided on the motor 144, a rod (not shown) extending in the horizontal direction in the case 145, and one end of the rod, and the shaft of the motor 144 rotates in the horizontal direction of the rod. A cam mechanism (not shown) that transmits the movement, a bellows type vacuum introduction terminal 146 provided at the other end of the rod, a flexible wire 147 that connects the vacuum introduction terminal 146 and the upper end of the pulling rod 143, and the flexible wire 147 are arranged horizontally. A pulley 148 that changes the direction between the vertical direction and the vertical direction, and a return spring 149. The lower end of the return spring 149 is in contact with the connecting portion 143c between the flexible wire 147 and the upper end portion 143b of the lifting rod 143, and the upper end of the return spring 149 is in contact with the element 149A.

  The first support mechanism 14 includes a support panel 14A fixed to one side wall of the main body casing 3 in a cantilever manner, and the upper frame 120c of the fixing portion 120 is connected to the lower surface of the horizontal plate 140A below the panel 14A. The electromagnetic actuator 142 that supports the rotating lever 141 is also supported by the panel 140A. Further, an element 149A that fixes the pulley 148 and the upper end side of the return spring 149 is also supported by the panel 140A.

  The motor 144 moves the vacuum introduction terminal 146 toward the left side in the drawing, whereby the flexible wire 147 connected to the vacuum introduction terminal 146 is pulled, and its direction is changed to an upward movement by the pulley 148 and pulled up. The rod 143 is pulled up. The rotational force of the motor 144 is converted into a linear motion by a cam and a link (not shown) built in the case 145, and the lifting rod 143 is moved up and down. The cam and the link will be described in the horizontal gravity gradient measuring device described later. After the movable portion 121 in the lower position (FIG. 5) is pulled up to the upper position (FIG. 4), the pulling rod 143 is moved down to the lowest position. Here, the wire 147 is pulled by the tension of the return spring 149. Is always in tension.

  The operation of the first support mechanism, that is, the free fall and return operation of the first free fall body 1 will be described. Now, as shown in FIG. 4, it is assumed that the movable part 121 is in the upper position, and the first free-falling body 1 is suspended from the movable part 121. In this state, the lifting rod 143 moves downward by the cam / link mechanism accompanying the rotation of the motor 144. By applying a predetermined voltage to the piezoelectric element 160, the piezoelectric element 160 extends upward, and the first free fall body 1 is lifted upward via the support portion 16. Note that the piezoelectric element 160 may be extended before the pulling rod 143 moves downward. When releasing the first free-falling body 1, a voltage that slowly increases is once applied to keep the piezoelectric element 161 extended to the maximum (while keeping the voltage), and the moment of release. The voltage is rapidly reduced to 0V. When the first free-falling body 1 is released, the electromagnetic actuator 142 forcibly rotates the proximal end side of the rotation locking lever 141 upward and rotates the locking claw 141a on the distal end side in the lateral direction. To release the locking state between the locking claw 141 a of the rotation locking lever 141 and the claw part 121 g of the movable part 121, and the movable part 121 is first dropped by the spring force of the push spring 140. Slide downward at a faster acceleration than the body 1.

  Here, the release means that the support portion 16 of the movable portion 121 is contracted, and 10 micrometers between the small ball 161 at the upper end of the support portion 16 and the lower surface of the upper frame 11c of the suspension portion 11 of the first free-falling body 1. A gap of a certain degree is formed, and the locking state between the locking claw 141a of the rotation locking lever 141 and the claw part 121g of the movable part 121 is short in a short time during which the first free-falling body 1 freely falls. The driving timing of the electromagnetic actuator 12 and the driving timing of the piezoelectric element 16 are adjusted so as to be released. The inertial mass of the movable part 121 and the strength of the push spring 140 are appropriately determined in consideration of the fall acceleration. In the illustrated embodiment, the piezoelectric element 160 is provided on the support portion 16 that supports the first free-falling body 1. However, in the case where there is a problem due to a short driving distance of the piezoelectric element 160, the movable portion By incorporating a piezoelectric element into a part of each of the 121 side frames 121a and 121b, a structure in which a piezoelectric element having a longer driving distance can be used can be obtained.

  The movable part 121 moved downward is stopped when the claw parts 121f and 121g formed at the upper ends of the side frames 121a and 121b come into contact with the upper ends of the dampers 120d and 120e. In the meantime, the first free fall body 1 falls freely and comes into contact with the small ball 161 at the upper end of the support portion 16 of the movable portion 121 at the lower position and stops. In this state, the first free-falling body 1 is in a state of being hung from the movable part 121 located at the lower position.

  By pulling up the lifting rod 143 by the driving means, the movable portion 121 and the first free fall body 1 are moved upward. The movable portion 121 is pulled up to the position of the locking claw 141a of the rotation locking lever 141 by pulling the suspension rod 5 upward by the vacuum introduction terminal, and the locking claw 141a of the rotation locking lever 141 is pulled up to the claw portion. By being locked to 121g, it is held in that position. At this time, by de-energizing the electromagnetic actuator, the rotation locking lever 141 is returned to the horizontal posture by a spring (not shown), and the inclined surface of the claw portion 121g is moved in accordance with the upward movement of the movable portion 121. Is automatically engaged while being guided by contact with the inclined portion of the claw portion 141a. When the movable portion 121 is fixed at the upper position, the lifting rod 143 moves downward, and when the movable portion 121 moves downward, the movable portion 121 and the lifting rod 143 are prevented from colliding.

  The second support mechanism 15 is a mechanism that supports the movable part of the second suspension mechanism 13 so as to be movable up and down, and is more effective than the free fall of the second free fall body 2 when the second free fall body 2 is released. The movable part is moved downward with a large acceleration, and after the second free-falling body 2 is freely dropped, the movable part at the lower position is moved up to the upper position together with the second free-falling body 2 suspended by the movable part. It is configured to let you. For the specific configuration of the second support mechanism 15, the description of the first support mechanism described above can be used. By controlling the first support mechanism and the second support mechanism so that the first free fall body 1 and the second free fall body 2 fall free at the same time, an interference fringe is obtained using a Michelson interferometer. Get vertical gravity gradient.

  In the vertical gravitational gradient measuring apparatus, an optical system in which the light beam is directed upward from the beam splitter 5 of the lower first free-falling body 1 is employed, so that the first suspension mechanism 12 and the first support mechanism 14 perform the first operation. (2) It is necessary to prevent the optical path of the light beam toward the reflecting mirror 4B of the free-falling body 2 from being obstructed. It will be understood by those skilled in the art that this can be solved by designing the size and shape of each mechanism and component, and the layout. For example, it is possible to form beam holes in the components of the first suspension mechanism 12 and the first support mechanism 14 so as to secure a portion corresponding to the reciprocating optical path of the light beam. In FIG. 1, the second support mechanism 15 of the second free-falling body 2 is also taken out from the side wall of the main body casing 3 in the same manner as the first support mechanism 14, but the second support mechanism of the second free-falling body 2 is You may make it hang from the upper wall of the main body casing 3 (refer FIG. 7 thru | or FIG. 9).

  Next, a horizontal gravity gradient measuring device will be described with reference to FIGS. In the horizontal gravity gradient measuring apparatus shown in FIGS. 6 to 9, the description of the vertical gravity gradient measuring apparatus is used for members having the same reference numerals as those of the vertical gravity gradient measuring apparatus shown in FIGS. can do.

  As shown in FIG. 6, the first free-falling body 1 and the second free-falling body 2 are disposed in the ultra-high vacuum portion 3 </ b> A of the main body case 3 with an interval in the horizontal direction. The first free fall body 1 is suspended from a first suspension mechanism 12, and the first suspension mechanism 12 is supported by a first support mechanism 14. The second free fall body 2 is suspended from the first suspension mechanism 13, and the first suspension mechanism 13 is supported by the first support mechanism 15. In the vertical gravity gradient measuring device, the first support mechanism 14 and the second support mechanism 15 are attached to the side wall of the main body case 3, whereas in the horizontal gravity gradient measuring device, the first support mechanism 14 and the second support mechanism. 15 is attached to the upper wall of the main body case 3. The light beam emitted from the laser light source 7 disposed in the atmospheric pressure portion 3B is directed upward by the reflecting mirror 6B, introduced into the ultrahigh vacuum portion 3A through the optical window 30c, and the beam splitter of the first free fall body 1 5, the light beam is divided into an upward light beam and a left light beam. The light beam traveling horizontally to the left is reflected by a reflecting mirror (for example, a corner cube prism) 4B of the second free-falling body 2. The upward light beam is reflected by a reflecting mirror (for example, a corner cube prism) 4A of the first free-falling body 1, and the reflected light beams are again combined by the beam splitter 5 to cause interference. The interference light is directed downward by the reflecting mirror 6A, introduced into the atmospheric pressure portion 3B through the optical window 30c, and directed horizontally by the reflecting mirror 6C, and then enters the photodetector 7, where it is converted into an electrical signal and amplified. And recorded after appropriate AD conversion.

  The release mechanism from the movable part of the first free fall body 1 and the second free fall body 2 is the same as the release mechanism of the vertical gravity gradient measuring device, and the description related to FIGS. 3 and 3 can be used. it can.

  The free fall and return operation | movement of the 1st free fall body 1 is demonstrated based on FIG. 7 thru | or FIG. Now, as shown in FIG. 7, it is assumed that the movable part 121 is in the upper position, and the first free-falling body 1 is suspended from the movable part 121. From this state, by transmitting a drive signal from the control unit 144a to the motor 144, the cam 150 rotates in conjunction with the rotation shaft of the motor 144, and the link 151 that engages with the cam 150 moves downward, thereby The pulling rod 143 moves downward through the introduction terminal 146 (FIG. 8).

  By applying a predetermined voltage to the piezoelectric element 160, the piezoelectric element 160 extends upward, and the first free fall body 1 is lifted upward via the support portion 16. The state in which the piezoelectric element 160 is extended to the maximum is maintained, and the voltage is suddenly reduced to 0 V at the moment of release. When the first free-falling body 1 is released, the electromagnetic actuator 142 forcibly rotates the proximal end side of the rotation locking lever 141 upward and rotates the locking claw 141a on the distal end side in the lateral direction. To release the locking state between the locking claw 141 a of the rotation locking lever 141 and the claw part 121 g of the movable part 121, and the movable part 121 is first dropped by the spring force of the push spring 140. Slide downward at a faster acceleration than the body 1.

  The movable part 121 moved downward is stopped when the claw parts 121f and 121g formed at the upper ends of the side frames 121a and 121b come into contact with the upper ends of the dampers 120d and 120e. In the meantime, the first free fall body 1 falls freely and comes into contact with the small ball 161 at the upper end of the support portion 16 of the movable portion 121 at the lower position and stops (FIG. 9). In this state, the first free-falling body 1 is in a state of being hung from the movable part 121 located at the lower position.

  By transmitting a drive signal from the control unit 144a to the motor 144, the cam 150 rotates in conjunction with the rotation shaft of the motor 144, and the link 151 engaged with the cam 150 moves upward, so that the vacuum introduction terminal 146 is moved. Accordingly, the pulling rod 143 is lifted upward to move the movable portion 121 and the first free fall body 1 upward. The movable portion 121 is pulled up to the position of the locking claw 141a of the rotation locking lever 141 by moving the lifting rod 143 upward, and the locking claw 141a of the rotation locking lever 141 is locked to the claw portion 121g. Is held in that position.

  The second support mechanism 15 is a mechanism that supports the movable part of the second suspension mechanism 13 so as to be movable up and down, and is more effective than the free fall of the second free fall body 2 when the second free fall body 2 is released. The movable part is moved downward with a large acceleration, and after the second free-falling body 2 is freely dropped, the movable part at the lower position is moved up to the upper position together with the second free-falling body 2 suspended by the movable part. It is configured to let you. For the specific configuration of the second support mechanism 15, the description of the first support mechanism described above can be used. By controlling the first support mechanism and the second support mechanism so that the first free fall body 1 and the second free fall body 2 fall free at the same time, an interference fringe is obtained using a Michelson interferometer. Get the horizontal gravity gradient.

  Some of the components of the gravity gradient measurement device can be shared by the vertical gravity gradient measurement device and the horizontal gravity gradient measurement device. The main body 10 of the first free-falling body 1 is provided with a first housing part 100 and a second housing part 101, and the first reflecting mirror 4A can be inserted into the housing parts 100 and 101 so as to be freely inserted and removed. Has been. When the first reflecting mirror 4A is located in the first housing part 100 (measurement of vertical gravity gradient), the first reflecting mirror 4A is arranged to reflect the light beam from the horizontal direction, and the first reflecting mirror 4A is disposed in the second housing part 101. When it is located inside (horizontal gravity gradient measurement), it is arranged to reflect the light beam from the vertical direction.

The main body 20 of the second free-falling body 2 is provided with two suspension portions 21 and 22 that extend orthogonal to each other so that the suspension portions 21 and 22 can be attached to and detached from the movable portion. It can be disassembled. In the vertical gravity gradient measurement device, the second free fall body 2 is suspended from the suspension portion 21, and in the horizontal gravity gradient measurement device, the second free fall body 2 is suspended from the suspension portion 22. The projecting portion 23 is an element having the same shape and weight as the suspension portion 22, and balances when the second free fall body 2 is suspended from the suspension portion 21. You may comprise the protrusion part 23 from the suspension part which can be attached or detached with respect to a movable part. If each component of the gravity gradient measuring device is configured to be detachable from the main body casing 3, only a main body casing for vertical gravity gradient measurement and a main body casing for horizontal gravity gradient measurement are prepared. Elements can be shared. Alternatively, if a main body casing having a large height of the ultra-high vacuum part 3A is used, only the mounting position and arrangement mode of other components are changed,
A device capable of measuring a gravity gradient for both vertical and horizontal can be configured.

  The gravity gradient measuring devices disclosed in Patent Documents 2 to 6 all relate to the measurement of the vertical gravity gradient. Then, the application of the horizontal gravity gradient measuring apparatus which is one aspect of this invention is demonstrated. First, there is an application to resource exploration. When the earth is spherically symmetric, the horizontal acceleration is zero, but the mass distributed locally in the sea and in the ground not only changes the vertical gravitational acceleration but also the horizontal gravitational acceleration. appear. In the case of the oblique direction, the size is comparable to the size in the vertical direction. Combined with the acceleration measurement data in the vertical direction, more accurate resource exploration becomes possible. Also, in geophysical measurement, high-quality information can be obtained by combining it with measurement data in the vertical direction, similar to the above resource exploration. Furthermore, it can also be applied to weight estimation of large moving objects and the like. In order to measure the weight of a large lorry on a highway, it is necessary to stop and place it on a scale, but it is possible to estimate the total weight by measuring the gravitational gradient in the horizontal direction. Similarly, it is possible to provide data capable of estimating the weight of a heavy object on the order of 10 tons loaded and unloaded on a cargo ship without placing it on a scale. However, it is necessary to know the shape and the distance to the object to be measured. Similarly, it can be applied to estimate the weight of large buildings and the weight of the contents of oil tanks. In this case as well, it is necessary to know the shape and the distance to the object to be measured, but it is useful when it is impossible to place it on the scale.

  The gravity gradient measuring device of the present invention has been described based on a vertical gravity gradient measuring device and a horizontal gravity gradient measuring device. A gravimeter that can be mounted on a carrier for resource exploration and geophysical surveys and can measure a wide range in a short time can only produce an accuracy of 50 microgal at best, but this method replaces acceleration measurement with gravitational gradient measurement. Therefore, it is possible to increase the measurement accuracy to 1 micro Gal or more. The present invention is suitable for gravity measurement which is mounted on a mobile body having acceleration, such as an airplane or a ship, for the purpose of performing resource exploration, active fault exploration or the like from the air or on the ship.

  The present invention can be used as a gravimeter. Examples of applications of gravity gradiometers include exploring resources sleeping on the ocean floor, exploring resources sleeping on land, finding dangerous hidden faults, and monitoring volcanic magma motion. This will be described more specifically. According to the present invention, there is a possibility that a place where mineral resources and energy resources are buried can be found more efficiently than before. This is because it is possible to estimate reserves from the sky with an unprecedented precision by aircraft. In addition, because unknown fault candidates can be surveyed in a short period of time, there is an expectation that installation of a nuclear power plant at risk can be easily avoided. It is also effective from the viewpoint of disaster prevention because it can provide precise information on the movement of the magma of the volcano just before the eruption.

1 is an overall view of a vertical gravity gradient measuring device according to the present invention. It is a figure which shows the optical system of the vertical gravity gradient measuring apparatus which concerns on this invention. It is a fragmentary figure explaining the suspension structure of a 1st free fall body. It is a figure which shows the 1st suspension mechanism and 1st support mechanism of the vertical gravity gradient measuring apparatus which concern on this invention, and has shown the state which has a movable part in an upper position. In FIG. 4, the first free-falling body is omitted. It is a figure which shows the 1st suspension mechanism of the vertical gravity gradient measuring apparatus which concerns on this invention, and a 1st support mechanism, and has shown the state which has a movable part in a lower position. In FIG. 5, the first free-falling body is omitted. 1 is an overall view of a horizontal gravity gradient measuring apparatus according to the present invention. It is a figure which shows the 1st suspension mechanism of the horizontal gravity gradient measuring apparatus which concerns on this invention, and a 1st support mechanism, and has shown the state which has a movable part in an upper position. In FIG. 7, the first free-falling body is omitted. It is a figure which shows the state which the pulling-up rod moved down from the state of FIG. It is a figure which shows the 1st suspension mechanism of the horizontal gravity gradient measuring apparatus which concerns on this invention, and a 1st support mechanism, and has shown the state which has a movable part in a lower position. In FIG. 9, the first free-falling body is omitted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st free fall body 10 Main body 11 Suspension part 2 2nd free fall body 20 Main body 21 Suspension part 3 Main body casing 3A Ultra-high vacuum part 3B Atmospheric pressure part 4A 1st reflective mirror 4B 2nd reflective mirror 5 Beam splitter 7 Laser light source 8 Photo detector 9 Gravity gradient acquisition means 12 First suspension mechanism 120 Fixed portion 121 Movable portion 13 Second suspension mechanism 14 First support mechanism 15 Second support mechanism

Claims (14)

A first free-falling body comprising a first reflecting mirror;
A second free-falling body provided with a second reflecting mirror;
A first suspension mechanism comprising: a fixed portion; and a movable portion movable up and down between an upper position and a lower position with respect to the fixed portion, and a first free-falling body suspended from the movable portion. ,
A second suspension mechanism comprising: a fixed portion; and a movable portion that can move up and down between an upper position and a lower position relative to the fixed portion, and a second free-falling body is suspended from the movable portion. ,
A first release mechanism for releasing the first free-falling body from the movable part of the first suspension mechanism in the upper position;
A second release mechanism for releasing the second free-falling body from the movable part of the second suspension mechanism in the upper position;
A mechanism for moving the movable part of the first suspension mechanism up and down, wherein when the first free-falling body is released, the movable part is moved down with an acceleration larger than the free fall of the first free-falling body, and the first free-falling body A first support mechanism configured to move the movable part at the lower position to the upper position together with the first free faller suspended by the movable part after the free fall;
A mechanism for moving the movable part of the second suspension mechanism up and down, wherein when the second free-falling body is released, the movable part is moved down with an acceleration larger than the free fall of the second free-falling body, and the second free-falling body A second support mechanism configured to move the movable part at the lower position to the upper position together with the second free-falling body suspended by the movable part after the free fall;
At least a casing for accommodating the first free fall body and the second free fall body in a vacuum state;
A light source;
When the first free-falling body and the second free-falling body are free-falling, the light beam emitted from the light source is directed to the first reflecting mirror and the second reflecting mirror, respectively. An optical system constituting a Michelson interferometer that generates interference of both reflected light beams from two reflecting mirrors;
A photodetector for receiving the interference light generated by the optical system;
Means for obtaining a gravitational gradient from the interference light received by the photodetector;
Consist of,
Gravity gradient measuring device.   The first free-falling body further includes a beam splitter, and the first free-falling body and the second free-falling body use the beam splitter to transmit the light beam emitted from a light source to the first reflecting mirror, Each of the second reflecting mirrors is directed so that the beam splitter receives the reflected light beams from the first reflecting mirror and the second reflecting mirror and generates interference between the reflected light beams. Item 4. The gravity gradient measuring device according to Item 1.   Each of the first release mechanism and the second release mechanism includes a piezoelectric element provided in each movable portion, and after extending each piezoelectric element and moving each free-falling body according to voltage application, The gravity gradient measuring device according to any one of claims 1 and 2, configured to release each free-falling body from a movable part of each suspension mechanism by extending and contracting instantaneously.   The gravitational gradient measuring device according to claim 3, wherein each of the piezoelectric elements is provided in a support portion where each movable portion supports each free-falling body.   5. The gravity gradient measuring device according to claim 4, wherein each movable part is a quadrilateral frame, and the support part is formed on a horizontal lower frame of the quadrilateral frame.   The piezoelectric element is arranged so that each movable part extends upward at each movable part, and each free fall body suspended from each movable part by extending the piezoelectric element. The gravity gradient meter device according to any one of claims 3 to 5, wherein the device is configured to move the height of the gravity gradient meter upward.   The gravity gradient measuring device according to claim 6, wherein each movable part is a quadrilateral frame, and the piezoelectric elements are provided on left and right side frames of the quadruple frame.   The gravity gradient measuring device according to any one of claims 1 to 7, wherein each free-falling body is suspended from each movable part by point contact. Each support mechanism
Means for urging each movable part in the upper position toward the lower side;
A locking means that is detachable with respect to each movable part in the upper position, and holds the movable part in the upper position;
Means for moving each movable part from the lower position to the upper position;
The gravity gradient measuring device according to claim 1, comprising:   The gravity gradient measuring device according to claim 9, wherein the upward movement means includes a lifting rod connected to each movable portion, and a driving means for moving the lifting rod upward.   The said 1st free fall body and the said 2nd free fall body are arrange | positioned at intervals in the perpendicular direction, and are comprised so that a vertical gravity gradient may be measured. Gravity gradient measuring device.   The said 1st free fall body and the said 2nd free fall body are arrange | positioned at intervals in the horizontal direction, and are comprised so that a horizontal gravity gradient may be measured. Gravity gradient measuring device. In the falling body main body of the first free-falling body, two accommodating portions for accommodating the first reflecting mirror so as to be freely inserted and removed are formed,
When the first reflecting mirror is located in the first housing part, it reflects the light beam from the first direction,
When the first reflecting mirror is located in the second housing portion, the light beam from the second direction orthogonal to the first direction is reflected.
The gravity gradient measuring device according to claim 11. The falling body body of the second free-falling body is provided with a first hanging portion and a second hanging portion that extend in directions orthogonal to each other,
Each of the first suspension part and the second suspension part is detachable from the movable part,
When the second free fall body is suspended from the movable part via the first suspension part, the second reflecting mirror reflects the light beam from the first direction,
When the second free fall body is suspended from the movable part via the second suspension part, the second reflecting mirror reflects the light beam from the second direction orthogonal to the first direction. ,
The gravity gradient measuring device according to claim 11.

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