28 results about "Equidistant" patented technology

The invention discloses a three-dimensional curved surface pattern layering processing method based on parameterized segmentation, and aims to solve the problem of high-precision pattern processing on the surface of a curved surface by using a laser scanning galvanometer. The method comprises the following steps: firstly, importing a three-dimensional model, and carrying out parameterization processing to obtain a two-dimensional parameter domain; positioning a to-be-processed plane pattern in the two-dimensional parameter domain to form a complete two-dimensional geometric grid covering a pattern area, generating a three-dimensional pattern grid attached to a curved surface, and calculating a center normal vector of the three-dimensional pattern grid; then, generating an equidistant plane group on the surface of the curved surface, and calculating an intersection line of the plane and the three-dimensional pattern grid as a laser scanning track; and the five-axis linkage platform-galvanometer system is started for machining. Through the parameterization domain, distortion of curved surface pattern machining is effectively solved, machining uniformity is improved, and the method is particularly suitable for laser machining of large-scale or high-complexity curved surface patterns.

The invention discloses a composite shell structure topology and fiber angle optimization and equal-interval path generation method. The invention relates to the field of topological optimization and continuous fiber reinforced composite material additive manufacturing, and aims to solve the problem that continuous, equidistant and manufacturable fiber paths are difficult to obtain for a composite shell structure in the prior art. According to the method, based on isogeometric analysis and a Riisner-mindlin shell theory, with flexibility minimization as a target, topology and fiber angle collaborative optimization is carried out on a curved surface shell structure, and a macroscopic topology form and unit fiber orientation are obtained. And extracting an optimized structure boundary and mapping the optimized structure boundary to a parameter space, constructing a grey-scale map through a density field to identify a parameter space boundary, performing fairing by adopting an NURBS curve, and then mapping the optimized structure boundary back to a physical space to form a smooth space boundary. And extracting a structural skeleton in the parameter space and mapping the structural skeleton to a physical space. And based on the smooth boundary and the skeleton, generating a space fiber path meeting the equidistant requirement.

The application discloses a device and method capable of realizing all-around real-time monitoring of tunnel structure deformation. The device comprises multiple non-contact displacement sensors, a rotating support assembly, a three-dimensional space locator assembly, an inclination sensor and a control unit. The multiple non-contact displacement sensors are equidistantly arranged along tunnel walls on the same cross section of the tunnel and are fixed through the rotating support assembly; the rotating support assembly can realize scanning measurement along the cross section and the longitudinal direction of the tunnel. The three-dimensional space locator assembly is used for monitoring the position change of the base point of the sensor, the inclination sensor is used for accurately controlling the scanning angle of the first rotating assembly, and the control unit is responsible for coordinated control and data processing. The application integrates automatic scanning, multiple sensor data mutual verification, environmental compensation and remote monitoring functions, can realize real-time, continuous and accurate monitoring of various deformation parameters such as tunnel ellipticity, segment misalignment and cross section convergence, significantly improves the monitoring efficiency and precision, and guarantees the tunnel operation safety.

The invention relates to the technical field of tool path planning, and discloses a combined curved surface constant residual height fixed-axis machining tool path generation method and a storage medium, and the method comprises the steps: firstly, discretizing a combined curved surface into a triangular mesh, and calculating the height of a collision-free tool location point above a machining part through adaptive quadtree sampling; forming a net-shaped structure of a discrete three-dimensional configuration space; projecting the processing area to the space for cutting, and determining an effective processing area; taking the boundary of the area as an initial seed polygon, outwards expanding line segments of the boundary into a cylindrical surface in a limited range, intersecting the cylindrical surface with the configuration space to generate a next circle of equidistant cutter location points, connecting the equidistant cutter location points to form a new cutter path, and iterating the process until the processing area is filled. According to the method, tool path selfing is fundamentally eradicated, the method is completely independent of the normal direction of the curved surface, the method is not sensitive to the model quality, the interference-free and equal-residue-height high-quality tool path can be generated in a full-automatic and high-robustness mode, and the reliability, efficiency and quality of complex curved surface numerical control programming are greatly improved.

The invention aims to provide a flow separation prediction method based on a mechanical energy gradient, and belongs to the field of flow separation prediction. Comprising the following steps: inputting a physical field and geometric conditions; selecting a monitoring interval; generating curve equidistant points in the interval based on the monitoring interval; generating corresponding tangent lines and angles based on the equidistant points; according to the obtained tangent line and the corresponding angle, speed conversion of the corresponding monitoring point is completed in combination with an existing physical field, and the speed conversion comprises the tangential speed and the normal speed. According to the method, curve equidistant points can be divided in the monitoring interval, the angle of the corresponding position is obtained to correct the relative speed, and a plurality of corresponding speed molded lines are generated according to the curve equidistant points, so that the relative speed molded lines are compared under the condition that uniform curve intervals are ensured, and the effectiveness and rationality of speed molded line comparison are ensured.

The invention discloses a complex test scene perception and partition construction method based on a multi-modal large model, and belongs to the technical field of digital test verification of high-end equipment. According to the method, a scene description prompt is designed, a multi-modal large model is utilized to generate a 2D test scene image with an equidistant view angle, and images with consistent semantics are screened through similarity calculation. Secondly, extracting spatial positions, semantic information and three-dimensional geometric parameters of objects in the scene by adopting a detection segmentation model and a depth estimation technology, and generating a feature map fusing space and semantics; and finally, geometric and texture description of an object is generated based on a multi-modal large model, a 3D grid is constructed by using a 3D generation model, model parameters are adjusted through dense matching and iterative optimization, and category accuracy and spatial coherence are ensured. According to the method, the full-process automation from 2D scene generation to 3D refined reconstruction is realized, and the precision and efficiency of complex test scene construction are remarkably improved.

The invention relates to the technical field of ship manufacturing, in particular to a ship curved surface self-adaptive spraying control method and system.The method comprises the steps that a target ship curved surface is scanned, three-dimensional point cloud data of the surface of the target ship curved surface is obtained, curved surface reconstruction and curvature calculation are conducted, and the ship curved surface is dynamically divided into spraying sub-areas according to curvature change characteristics; for each spraying sub-region, matching an optimal initial spraying parameter set from a pre-stored spraying process parameter database, generating a spraying path which ensures that the tail end of a spraying gun keeps a constant optimal distance from the curved surface by adopting equidistant bias based on the geometrical characteristics of each sub-region, and planning a global movement sequence of a robot; and controlling the mobile robot platform and the spray gun to execute spraying operation, monitoring spraying state parameters in real time through a sensor in the execution process, comparing the spraying state parameters with expected values, and dynamically adjusting spraying parameters through closed-loop control so as to realize uniform coating coverage, dynamically adjust execution parameters and ensure the spraying quality.

The invention aims to provide a speed profile generation method based on relative coordinates, and belongs to the field of fluid analysis. Comprising the following steps: inputting a physical field and geometric conditions; selecting a monitoring interval; generating curve equidistant points in the interval based on the monitoring interval; generating corresponding tangent lines and angles based on the equidistant points; according to the obtained tangent line and the corresponding angle, speed conversion of the corresponding monitoring point is completed in combination with an existing physical field, and the speed conversion comprises the tangential speed and the normal speed. According to the method, curve equidistant points can be divided in the monitoring interval, the angle of the corresponding position is obtained to correct the relative speed, and a plurality of corresponding speed molded lines are generated according to the curve equidistant points, so that the relative speed molded lines are compared under the condition that uniform curve intervals are ensured, and the effectiveness and rationality of speed molded line comparison are ensured.

The present invention relates to a method for defining a path of a laying head (1) for laying a tyre assembly on a core (4), comprising a step (a) of geometrically characterizing a profile in which a first set of geometrically significant points (PP1,...PPn) is provided which represent the shape of the profile (10), a step (b) of functionally characterizing the profile in which a second set of functionally significant points (PF1,...PFm) is provided which are associated with laying rules which specify laying conditions of the tyre assembly and which are stored in a path table, a step (c) of gridding in which a series of equidistant virtual points called "potential guide points" (PG1,...PGp) is defined on the profile (10) from the first functionally significant point (PF1) to the last functionally significant point (PFm), followed by a step (d) of simplification in which the size of the path table is reduced by applying one or more selection criteria to the path table so as to select a portion of the potential significant points (PGk) and of the significant points (PPi, PFj).

This invention relates to the field of optical measurement and calibration technology, and in particular to a method, medium, and apparatus for calibrating a plane reference mirror in a vertical interferometer. The method involves placing a calibration plate as a temporary mirror under test in the measurement optical path of a vertical Fizeau interferometer. At at least one measurement point, the calibration plate is continuously rotated around its own rotation center. The rotation centers at each measurement point are offset from the central optical axis of the plane reference mirror and equidistant. Multiple frames of surface shape measurement data are collected at each measurement point, and the absolute surface shape error of the plane reference mirror is obtained by arithmetic averaging of all measurement point data. This method, through the specific offset measurement point settings, systematically changes the spatial orientation of the calibration plate at different points, offsetting central symmetry errors and suppressing asymmetric errors and random noise. It achieves high-precision and robust absolute calibration without the need for complex algorithms. Compared with traditional methods, it combines accuracy, efficiency, and practicality, is suitable for various application scenarios, and provides a framework for subsequent efficiency optimization.

This invention relates to the fields of vibration control and nonlinear mechanics, and provides a programmable method for generating two-dimensional nonlinear forces. The method includes: responding to a two-dimensional nonlinear force generation request; acquiring the structure and structural parameters of a mechanical realization device; determining the trajectory of the center point of a rolling component during motion based on mechanical equilibrium relationships, and acquiring the geometric expression of the rolling component's trajectory surface; and, based on the geometric dimensions of the rolling component, performing equidistant mapping along the normal direction on the rolling component's trajectory surface, causing the rolling component to adhere to and roll along a three-dimensional guide surface, thereby generating a nonlinear force corresponding to a target nonlinear force function. This method not only generates nonlinear forces of arbitrary continuous form based on a preset target force function and supports personalized customization of nonlinear stiffness characteristics, but also generates nonlinear forces that meet target requirements in two mutually orthogonal motion directions.

The invention discloses a generation method and device of a pipe gallery model, equipment and a storage medium, and the method comprises the steps: obtaining the curvature of each path point in a path of the pipe gallery model, and dividing the path into a straight line segment and a bent segment based on the curvature distribution of each path point; under the condition that the path is a straight line segment, position and direction transformation is conducted on a preset pipe gallery model based on a spatial transformation matrix, a first geometric model corresponding to the straight line segment is obtained, and the spatial transformation matrix comprises a rotation matrix and an offset matrix; under the condition that the path is the bent section, performing equidistant scanning section generation processing on a preset pipe gallery model based on the curvature to obtain a plurality of section units; performing space mapping processing on the plurality of section units to obtain a second geometric model corresponding to the bent section; and splicing the first geometric model and the second geometric model to obtain a target pipe gallery model. Therefore, manual operation can be reduced, and the modeling efficiency and precision are remarkably improved.

The application discloses a spherical sight line guidance method considering longitude mutation of the day boundary, and comprises the following steps: establishing a nonlinear mathematical model of ship movement; based on the nonlinear mathematical model of ship movement, establishing a ship guidance strategy under a spherical coordinate system, introducing a longitude normalization operator, and utilizing spherical trigonometry to solve a spherical geometric relation between the ship and a virtual target point, so as to obtain an expected great circle course of the ship; based on the nonlinear mathematical model of ship movement, a controller is designed by using a third-order closed-loop gain shaping algorithm, so as to control the ship to track the expected great circle course; and the navigation track of the ship on a real sphere is presented by equidistant azimuth projection, and an undistorted great circle navigation track of the ship across the ocean is output. Through simulation verification, the application can make the ship cross the day boundary stably and control the ship to navigate along the great circle course, and is helpful to green, safe and autonomous navigation of the ship.

1. The name of the design product: gear cover (five equidistant curve surface). 2. The use of the design product: for hydraulic rock drill gear box transmission. 3. The design points of the design product: in shape, especially the green profile surface is five equidistant curve surface. 4. The picture or photo that can best show the design points: design 1 perspective view 1. 5. Design 1 right view is symmetrical with design 1 left view, omit design 1 right view; Design 1 bottom view is symmetrical with design 1 top view, omit design 1 bottom view. 6. Design 1 is designated as the basic design.

The invention discloses a self-adaptive calibration method and system for an electric control handle structure, a storage medium and equipment. The method comprises the following steps: acquiring calibration parameters and an actual mechanical angle of a to-be-calibrated handle; based on the obtained calibration parameters and the actual mechanical angle, adopting an equidistant interval algorithm to generate angle coordinates of a plurality of calibration points covering the effective physical stroke of the to-be-calibrated handle; and according to the angle coordinates of the calibration points, driving the to-be-calibrated handle to sequentially stop at each calibration point and acquiring an output value of the sensor in the to-be-calibrated handle at each calibration point, and establishing a mapping relation between the output value of the sensor in the to-be-calibrated handle and a standard output value of the stroke of the handle to complete calibration. The method can adapt to the individual mechanical structure difference of the handle, and consistent and accurate control performance is obtained through calibration.

The invention relates to the field of automatic control, discloses an equidistant curve path generation and smoothing method, and is used for solving the problems of complex selfing detection and loop cutting calculation, poor real-time performance, unstable agricultural machinery operation caused by sudden change of sharp points and curvature of a generated path, and the like in the prior art. And the path precision, the calculation efficiency and the hardware cost are difficult to consider at the same time. Comprising the steps of performing normal offset according to a normal vector of a base curve and a set offset distance, preliminarily generating an equidistant curve point set, quickly performing local selfing detection by using a two-dimensional grid spatial index technology, generating a non-selfing path, and performing non-selfing detection on the basis of the actual minimum turning radius constraint of the agricultural machine. And a bidirectional iterative smoothing algorithm is adopted to eliminate sharp corners and curvature abrupt changes in the path, and fitting and interpolation densification are carried out on the path. According to the method, a smooth, continuous, selfing-free and two-order derivable high-quality operation path can be efficiently generated in real time, and the stability and the operation precision of agricultural machinery path tracking are remarkably improved.

The invention provides a complex curved surface additive cladding trajectory planning method and device based on a vector field, and the method comprises the steps: defining a parameterized model of coordinates and geometric attributes of all points of a curved surface structure of a remanufacturing region, selecting a working region with z-axis projection meeting a single mapping relation based on the parameterized model, defining a boundary, discretizing the working region into points, and obtaining the complex curved surface additive cladding trajectory. Constructing a tensor field representing the optimal machining direction of each point through an intersecting line direction vector by combining geometric attributes of each point of the parameterized model, solving a saddle point according to a preset condition, determining a type, screening a separation line to divide a working area into sub-blocks through circumferential interpolation, solving a sub-block tensor field streamline, and obtaining a sub-block tensor field; and a starting trajectory is selected to generate a trajectory covering the sub-blocks in an equidistant offset mode along a preset normal, and a remanufacturing area additive cladding trajectory is obtained through integration. Geometric data basis is unified through a parameterized model, processing characteristics are accurately adapted through a tensor field, sub-block processing suitability is optimized through saddle point segmentation, and a finally generated track can reduce adverse effects of gravity on a cladding process.

An automatic wire placement thickening curved surface modeling method based on a fast marching method comprises the steps that composite material design information serves as input, a mold curved surface is voxelized, and a distance field is efficiently calculated through the fast marching method; then voxel edges are traversed, an equidistant point set is obtained through linear interpolation, and an original equidistant curved surface is established by applying a triangulation algorithm; finally, the grid segmentation algorithm is used for cutting to obtain thickened and non-thickened area curved surfaces, the two curved surfaces are sewn, and the final thickened curved surface is obtained.Compared with a traditional curved surface offset method, the method has the advantages that the problem of layering surface modeling under the condition that the thickness of a large-curvature component is increased is effectively solved, controllable high calculation precision is achieved, and the calculation process is more stable.

The invention discloses an open caisson construction state recognition method and system based on multi-source data, and belongs to the technical field of open caisson construction. Establishing a three-dimensional model of the construction area, dividing multiple groups of fan-shaped symmetric construction tasks by taking the center point of the top surface as a symmetric point, performing synchronous construction, and collecting elevation value and inclination data; a two-dimensional coordinate system is constructed through equal-interval sampling, and two state curves corresponding to the elevation and the gradient are generated; a task-stage alternate circulation construction mode is adopted, tasks are scheduled based on a linear mapping relation, curve slope errors are evaluated in real time, and a non-uniform state is corrected; and after all tasks reach the standard, performing weighting processing with higher recent weight in combination with historical Euclidean distance data, calculating an accumulated error reference value and a current error influence degree, and outputting an error level. According to the invention, accurate identification, dynamic correction and scientific evaluation of the construction state can be realized, the problems of incomplete traditional construction state monitoring, error evaluation lag and the like can be solved, and the construction safety and the quality stability are improved.

This invention provides a parametric modeling method and system for a full model of a side-type inlet / outlet, relating to the field of hydraulic engineering technology. The method includes: generating a coordinate transformation matrix based on the engineering parameters and number of inlets / outlets; integrating and processing the two-dimensional control points of the inlet / outlet structure's outline with unit normals to obtain a homogeneous unit normal matrix, and determining equidistant offset lines tangent to the pier head arc of the inlet / outlet structure; generating two-dimensional control points for the pier head arc based on the equidistant offset lines; stacking all two-dimensional control points of the inlet / outlet structure into a control point matrix to generate a three-dimensional model of the inlet / outlet structure; combining the engineering parameters of other structures to generate three-dimensional models of other structures, and then combining the coordinate transformation matrix to generate a full model of the side-type inlet / outlet. This invention improves the speed of parametric modeling of a full model of a side-type inlet / outlet reservoir area and enhances the stability of the modeling process.

The application discloses a power transmission line ground inclination calculation method and device based on information entropy weight, and comprises the following steps: S1, constructing a three-dimensional scene; S2, sampling equidistantly left and right along the direction of the vertical line of the overhead line of each base tower, and obtaining the original slope value of each sampling point; S3, constructing an original slope value matrix R based on the original slope value of all sampling points on the left side or the right side; S4, performing normalization processing on the original slope value matrix R, and obtaining a normalized matrix R ′ ; S5, constructing a probability matrix P; S6, calculating the entropy value of each base tower in the probability matrix P; S7, calculating the slope value weight of each sampling point according to the entropy value; S8, modifying the original slope value by using the slope value weight, and obtaining the ground inclination on the left side or the right side of the tower; S9, selecting the other side of the vertical line of the tower to the overhead line, and repeating the process described in steps S3-S8, so as to calculate the ground inclination of the tower on the other side of each base tower. The application can improve the accuracy of ground inclination calculation.

The application relates to an air mixer, which relates to the technical field of air mixing devices. The air mixer comprises a shell, an air inlet end, an air outlet end and an airflow mixing channel. The airflow mixing channel comprises two airflow guide surfaces and two end surfaces. The airflow guide surfaces are formed by stretching corresponding contour lines in the front-rear direction. The contour lines are constructed as follows: three circles with aligned centers and equidistant distribution are constructed in a three-dimensional space, the diameters of the two circles on the sides are equal and larger than the diameter of the middle circle; a line segment passing through the two side circles and tangent to the middle circle is constructed, an axis passing through all the circle centers is constructed, the line segment is rotated around the axis for one turn, and the intersection line of the obtained curved surface and the plane passing through the axis is taken as the contour line of the two airflow guide surfaces. The airflow mixing channel surrounded by the two airflow guide surfaces and the two end surfaces constructed in a specific manner can mix multiple airflows, and the uniformity and consistency of the mixed air are better.

The invention provides a hole axis measuring device and a hole axis measuring method. The device comprises a sleeve, a measuring reference structure and a plurality of telescopic structures, the positioning sleeve is used for being inserted into a to-be-detected hole; the telescopic structures are arranged in the positioning sleeve in the radial direction of the positioning sleeve, can synchronously extend out of the side wall of the positioning sleeve at equal intervals in the radial direction of the positioning sleeve and abut against the side wall of the to-be-detected hole, so that the axis of the positioning sleeve coincides with the axis of the to-be-detected hole; the measurement reference structure is arranged at the top of the positioning sleeve, and the axis of the measurement reference structure coincides with the axis of the positioning sleeve; wherein the measurement reference structure is used for being scanned by a scanning device to obtain point cloud information, and the space parameters of the axis of the to-be-measured hole are determined according to the point cloud information. The method has high accessibility, the technical effect of efficiently measuring the axis of the to-be-measured hole is achieved, and the cost of hole axis measurement is greatly reduced.

The invention belongs to the technical field of path planning, and particularly relates to a slope field driven curved surface layering 3D printing path planning method and system, and the method comprises the steps: obtaining a to-be-printed curved surface structure model and a triangular patch file of a reference surface of the to-be-printed curved surface structure model; performing orthographic projection on the curved surface structure model to obtain an orthographic projection model; performing hierarchical slicing on the orthographic projection model according to the layering thickness, and dividing the range of each slicing layer; establishing a plurality of equidistant parallel intersecting surfaces, intersecting with the reference surface, calculating to obtain three-dimensional intersection point coordinates, calculating a slope field value of any two adjacent intersection points in the same intersecting surface, and constructing a slope field of the reference surface; projecting a reference plane slope field into each divided slice layer range, constructing a slope field of each slice layer, and extracting equidistant path points in each slice layer; generating path planning of an orthographic projection model according to the equidistant path points, and generating orthographic projection model path points; and performing inverse projection transformation on the orthographic projection model path points to obtain a path of the to-be-printed curved surface structure model.

The invention discloses a modeling method for a composite lattice sandwich propeller blade CAE model, and belongs to the field of ship propulsion technology and advanced composite structure design. The method comprises the following steps: 1, constructing a three-dimensional geometric model of lattice unit cells; 2, reconstructing a blade entity model based on the geometric shape value point data of the target propeller, and determining a designed space boundary and a reference shape; 3, generating a first equidistant curved surface and a second equidistant curved surface on the inner side of the paddle solid model from outside to inside, and dividing the paddle solid model into a composite panel domain, a layering base domain and a dot matrix sandwich domain; fourthly, Boolean intersection operation is conducted on the remaining dot matrix cell element array located in the dot matrix sandwich domain, and a dot matrix sandwich structure precisely attached to the boundary of the dot matrix sandwich domain is obtained; and 5, performing Brinell addition operation on the composite material panel domain, the laying layer base domain and the lattice sandwich structure to form a complete composite material lattice sandwich propeller blade CAE (Computer Aided Engineering) model. The method is used for modeling the CAE model of the composite lattice sandwich propeller blade.

The geometric diagraph comprises a central transverse rod and a central vertical rod which are vertically crossed with each other, and the intersection point of the central transverse rod and the central vertical rod forms an original point of a coordinate system. A plurality of parallel cross rods are symmetrically arranged on the two sides of the center cross rod, and a plurality of parallel vertical rods are symmetrically arranged on the two sides of the center vertical rod. The appliance is provided with a two-way equidistant adjusting mechanism which comprises a transverse adjusting mechanism connected with the central vertical rod and the parallel vertical rods respectively and a vertical adjusting mechanism connected with the central transverse rod and the parallel transverse rods. The two-way equidistant adjusting mechanism can synchronously drive the parallel rod pieces to expand from the center rod to the two sides at equal intervals. The invention aims to provide the geometric diagraph so as to realize multi-vertex same-reference positioning of geometric figures and effectively reduce accumulative errors generated in the drawing process.

The invention discloses a discrete equidistant immersion three-dimensional reconstruction method and system based on curved surface measurement, and the method comprises the following steps: calculating an interior angle and an initial edge vector based on an input triangular mesh and side length, constructing a discrete contact and spin structure, constructing an anisotropic energy function after a symbol is corrected through topological decomposition, and constructing a discrete contact and spin structure; optimizing the rotation direction through semi-implicit gradient descent; further constructing an edge vector field, taking divergence as a right end item of a Poisson equation, and solving by a conjugate gradient method to obtain a three-dimensional coordinate; and finally, constructing an optimization function through target curvature constraint, and optimizing the geometric shape in combination with a local-global method. According to the method, the geometric accuracy and visual reality of reconstruction are remarkably improved through a curvature constraint mechanism.

To provide a displacement measuring device and a displacement measuring method that can directly measure displacement including a ground subsidence amount at a foundation bottom level.SOLUTION: A first measurement unit A includes a reference anchor 16 fixed to a back side of a first borehole 14, a first rod 20, and first displacement meters 18A to 18D fixed to a hole wall of the first borehole 14 around an extended end side of the first rod 20 and measuring an axial displacement of the first rod 20. A second measurement unit B includes a fixing portion 32 fixed to an entrance side of a second borehole 28, a second rod 34 extending from the fixing portion 32 towards a back side of the second borehole 28, and a second displacement meter 30 fixed to a hole wall of the second borehole 28 around an extended end side of the second rod 34 and measuring an axial displacement of the second rod 34. The first displacement meter 18A and the second displacement meter 30 are provided at positions equidistant from a predetermined reference plane.SELECTED DRAWING: Figure 1