CN102494657B  Measuring head radius compensation method for curve surface profile measuring and detecting  Google Patents
Measuring head radius compensation method for curve surface profile measuring and detecting Download PDFInfo
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 CN102494657B CN102494657B CN201110412612.8A CN201110412612A CN102494657B CN 102494657 B CN102494657 B CN 102494657B CN 201110412612 A CN201110412612 A CN 201110412612A CN 102494657 B CN102494657 B CN 102494657B
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Abstract
Description
Technical field
The present invention relates to measurement and the detection method of curve surface work pieces outline line, relate in particular to a kind of Proberadius Compensation in Reserve method of curved surface profile measurement and detection.
Background technology
A kind of means of manufacturing as product design, in early 1990s, reverseengineering starts to cause the great attention of various countries' industry member and academia, hereafter, about being just subject to people with application always, the research of reverseengineering pays close attention to, particularly, along with the development of the present computer technology and measuring technology, the reverseengineering of utilizing CAD/CAM technology, advanced manufacturing technology to realize product material object has become a study hotspot in CAD/CAM field, and becomes the main contents of reversal technique application.It is two gordian techniquies of reverse modeling that the digitizing of part and cad model are rebuild.
Implement reverseengineering, first will extract the threedimensional coordinate information of subject surface, the measuring method that reverseengineering adopts is mainly divided into two large classes: contact and contactless.In the time adopting contact measuring head to measure, due to the impact of gauge head radius, the coordinate data obtaining not is the coordinate of the surface point that touches of gauge head, but the coordinate of the gauge head centre of sphere, when the surperficial direction of normal of measured point with survey direction of principal axis when consistent, measuring point coordinate and gauge head center differ a gauge head radius value.Conventionally gauge head radius is between 0.25mm～20mm, if ignore gauge head radius, the data that obtain are not carried out radius compensation processing, will cause measuring error.In the time that the pressure of gauge head is vowed (surperficial method arrow) and measured cross section on a plane, measurement point curve is plane curve; In the time that the pressure of gauge head is vowed (surperficial method arrow) and measured cross section not on a plane, measurement point line is space curve.In general, reconstruction model is all bigger than normal in prototype in kind, and in the time that the accuracy requirement of reverse model is higher, reply measurement data is carried out gauge head compensation.
In measuring, CMM (three coordinate measuring machine) extensively adopts at present twodimentional automatic compensating method, in the time measuring, measurement point and gauge head radius relationship are all processed into twodimentional situation, and compensation is calculated and enrolled in process of measurement, in the time measuring, automatically complete the gauge head compensation of data.Compensation calculating has been simplified in this compensation method, do not affect to measure to adopt a little and sweep velocity, and the surface measurement that some are made up of regular shape, plane, quadric surface etc., two dimension compensation is accurate.But for the compound curved surface of some free form surface compositions, when measurement, the Surface Method of point position is vowed conventionally and surveys axle not in same plane, now error can be there is by two dimension compensation, in the situation that error can not be ignored, the threedimensional compensation of gauge head radius must be considered measurement data to carry out.
Summary of the invention
The present invention has designed and developed a kind of Proberadius Compensation in Reserve method of curved surface profile measurement and detection.In the present invention, utilize gauge head to get a little along the scanning of cross section profile marking line, form gauge head outline line point cloud, and at sweep trace of each side increase of cross section profile marking line, for near the nearest some points of selected distance any point P in gauge head outline line point cloud, and construct fit Plane, vow the survey radius of a ball compensation P ' that realizes some P by fit Plane method.Utilize the method after projection is calculated, can obtain design attitude (measuring wheel profile cloud data.Measuring accuracy of the present invention is high, especially can meet and have the outline line measurement of complexcurved largescale workpiece and the requirement of quality testing.
Technical scheme provided by the invention is:
A Proberadius Compensation in Reserve method for curved surface profile measurement and detection, comprises the following steps:
Step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, form at least one left line point cloud and at least one right line point cloud;
Step 2, extract the some P in described gauge head outline line point cloud, from described gauge head outline line point cloud, extract at least two points nearest with some P, and from each described left line point cloud, all extract with described gauge head outline line point cloud in nearest at least one point of some P, from each described right line point cloud, all extract with described gauge head outline line point cloud in nearest at least one point of some P, form some group, utilize described some group fit Plane, and the method that obtains described fit Plane is vowed, a P is carried out to radius compensation along direction of normal, obtain radius compensation point P ',
Step 3, repeating step two, obtain the cross section contour point cloud being made up of the radius compensation point corresponding with point in described gauge head outline line point cloud.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilizing gauge head is one in the number of the sweep trace each side increasing of described cross section contour.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 2, from described gauge head outline line point cloud, extract a point that is positioned at a point in a P front and is positioned at a P rear, from a described left line point cloud, extract two points nearest with some P, from a described right line point cloud, extract two points nearest with some P.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, be achieved in the following ways:
By manual the cross section contour on the described workpiece for measurement surface cross section profile marking line that marks into, the reference measurement coordinate system of selected workpiece for measurement, make the coordinate axis of described cross section profile marking line place plane perpendicular to described reference measurement coordinate system, utilize gauge head to get a little along described cross section profile marking line scanning.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, form at least one left line point cloud and at least one right line point cloud, be achieved in the following ways:
Utilize gauge head to get a little along workpiece for measurement cross section profile line sweep, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, forms gauge head outline line point cloud,
Utilize each side increase by least one sweep trace of gauge head at described cross section contour, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, forms at least one left line point cloud and at least one right line point cloud.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along cross section profile line sweep, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, forms gauge head outline line point cloud
Utilize each side increase by least one sweep trace of gauge head at described cross section contour, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, forms at least one left line point cloud and at least one right line point cloud,
Wherein, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, is achieved in the following ways:
The surface of described workpiece for measurement or near selected reference point, and described system coordinate system and described reference measurement coordinate system have at least three reference points, described system coordinate system is converted into described reference measurement coordinate system by described at least three reference points.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, the number of the total reference point of described system coordinate system and described reference measurement coordinate system is more than four.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, described system coordinate system also comprise arrange around the surrounding of described workpiece for measurement, with at least system coordinate system of the system coordinate system in interval of described reference measurement coordinate system, and adjacent two system coordinate systems have at least three reference points, and described system coordinate system is converted into adjacent system coordinate system by least three the common reference points of system coordinate system that are adjacent.
Preferably, in the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, the number of the common reference point of described adjacent two system coordinate systems is more than four, and the number of the common reference point of described reference measurement coordinate system and the system coordinate system being adjacent is more than four.
The Proberadius Compensation in Reserve method of curved surface profile measurement of the present invention and detection utilizes gauge head to get a little along the scanning of cross section profile marking line, form gauge head outline line point cloud, and closely respectively increase a sweep trace in the left and right sides of cross section profile marking line, for near the nearest some points of selected distance any point P in gauge head outline line point cloud, and construct fit Plane, vow the survey radius of a ball compensation P ' that realizes some P by fit Plane method.Utilize the method after projection is calculated, can obtain the measuring wheel profile cloud data of design attitude.Measuring accuracy of the present invention is high, especially can meet and have the outline line measurement of complexcurved largescale workpiece and the requirement of quality testing.
Accompanying drawing explanation
Fig. 1 is the schematic flow sheet of curved surface profile measurement method.
Fig. 2 is the schematic diagram of the radius compensation of gauge head outline line point cloud mid point P.
Fig. 3 is the schematic diagram of cross section projection.
Fig. 4 is the schematic diagram that the mark of reference measurement coordinate system in embodiment is established.
Fig. 5 (a) is the vertical view of control points layout in embodiment.
What Fig. 5 (b) was control points layout in embodiment overlooks inclination figure.
Fig. 6 is the planning schematic diagram of embodiment middle section profile marking line.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in further detail, to make those skilled in the art can implement according to this with reference to instructions word.
As shown in Figure 1, the invention provides a kind of Proberadius Compensation in Reserve method of curved surface profile measurement and detection, comprise the following steps:
Step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, form at least one left line point cloud and at least one right line point cloud;
Step 2, extract the some P in described gauge head outline line point cloud, from described gauge head outline line point cloud, extract at least two points nearest with some P, and from each described left line point cloud, all extract with described gauge head outline line point cloud in nearest at least one point of some P, from each described right line point cloud, all extract with described gauge head outline line point cloud in nearest at least one point of some P, form some group, utilize described some group fit Plane, and the method that obtains described fit Plane is vowed, a P is carried out to radius compensation along direction of normal, obtain radius compensation point P ',
Step 3, repeating step two, obtain the cross section contour point cloud being made up of the radius compensation point corresponding with point in described gauge head outline line point cloud.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilizing gauge head is one in the number of the sweep trace each side increasing of described cross section contour.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 2, from described gauge head outline line point cloud, extract a point that is positioned at a point in a P front and is positioned at a P rear, from a described left line point cloud, extract two points nearest with some P, from a described right line point cloud, extract two points nearest with some P.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, be achieved in the following ways: by manual the cross section contour on the described workpiece for measurement surface cross section profile marking line that marks into, the reference measurement coordinate system of selected workpiece for measurement, make the coordinate axis of described cross section profile marking line place plane perpendicular to described reference measurement coordinate system, utilize gauge head to get a little along described cross section profile marking line scanning.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along the cross section profile line sweep of workpiece for measurement, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, form at least one left line point cloud and at least one right line point cloud, be achieved in the following ways: utilize gauge head to get a little along workpiece for measurement cross section profile line sweep, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, form at least one left line point cloud and at least one right line point cloud.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, in described step 1, utilize gauge head to get a little along cross section profile line sweep, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, form gauge head outline line point cloud, utilize each side increase by least one sweep trace of gauge head at described cross section contour, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, form at least one left line point cloud and at least one right line point cloud, wherein, the point that scanning is obtained is converted in reference measurement coordinate system by the system coordinate system of measuring system, be achieved in the following ways: described workpiece for measurement surface or near selected reference point, and described system coordinate system and described reference measurement coordinate system have at least three reference points, described system coordinate system is converted into described reference measurement coordinate system by described at least three reference points.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, the number of the total reference point of described system coordinate system and described reference measurement coordinate system is more than four.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, described system coordinate system also comprise arrange around the surrounding of described workpiece for measurement, with at least system coordinate system of the system coordinate system in interval of described reference measurement coordinate system, and adjacent two system coordinate systems have at least three reference points, and described system coordinate system is converted into adjacent system coordinate system by least three the common reference points of system coordinate system that are adjacent.
In the Proberadius Compensation in Reserve method of described curved surface profile measurement and detection, the number of the common reference point of described adjacent two system coordinate systems is more than four, and the number of the common reference point of described reference measurement coordinate system and the system coordinate system being adjacent is more than four.
Measure the outline of the largescale curved workpiece such as pneumatic equipment blades made, airframe, permissible accuracy is more and more higher on the one hand, needs on the other hand to carry out at the scene data acquisition fast.With regard to existing measurement means, with respect to systems such as other three coordinate measuring machines, photogrammetric, transit surveys, laser tracker measuring system has that precision is high, efficiency is high, measurement range is large, volume is little, be easy to carry, can carry out the advantages such as work on the spot, is particularly suitable for being not easy to the precision measurement of mobile largescale workpiece.Therefore, the present invention uses laser tracker measuring system.And, in gauge head scanning process, be handhold scanning.
1, the principle of work of laser tracker measuring system and measurement requirement
Laser tracker measuring system is mostly made up of laser tracking head, controller, computing machine, reverberator (gauge head) and measurement annex etc.Its basic functional principle is, follower head Emission Lasers is followed the tracks of reverberator, twin shaft angle measuring system and range measurement system by instrument calculate the locus of reverberator in spherical coordinate system, recycling instrument calibration parameter and meteorological sensor compensate systematic error and atmospheric environment error, obtain accurate volume coordinate.Wherein range measurement system is made up of the laser interference stadimeter (IFM) of Relative ranging and the device (ADM) of absolute distance measurement, light as disconnected in generation in tracing process, and the latter can be used for recovering to measure.
The metering system of laser tracker comprises static object measurement, dynamic target tracking measurement etc.Static object measurement has the modes such as singlepoint average measurement, matching measurement or hidden place measurement.Dynamic tracking measurement by laser tracker peculiar, can by set time or apart from interval continuous sampling.
Laser tracker has higher measuring accuracy, and take the T3 of API as example, radius 60m, IFM measuring accuracy 0.5 μ m/m, ADM measuring accuracy 15 μ m, angle measurement accuracy 3.5 μ m/m are followed the tracks of in instrument nominal.But these precision indexs of instrument are not definitely constant, itself and measurement environment, instrument self stability, tracking range etc. are closely related.Air pressure in measurement environment, temperature, humidity, even vibration not only can affect the performance of instrument itself, and workpiece for measurement is also had to larger impact, and there is larger difference in the measurement result under varying environment therefore sometimes.The stability requirement of instrument must be calibrated and fully preheating before use.The software kit of general instrument all provides calibration function, and instrument, after transportation or measurement environment change, all needs to recalibrate.Due to the highaccuracy property of instrument, warm causes that apparatus structure slight change will affect the precision of instrument, thereby requires highprecision measurement must carry out abundant preheating.In addition, also need to consider measuring distance and the impact of angle on measurement result, generally speaking measuring distance is nearer, the less precision of angle measurement is higher.
The measuring principle of comprehensive above laser tracker and affect the factor of laser tracker measuring accuracy, requirement in the time carrying out highacruracy survey: within (1) measuring distance remains on limited field as far as possible, this has not only shortened measuring distance, and has reduced the scope of angle measurement; (2) to guarantee the fixing of laser tracker and workpiece for measurement; (3) guarantee that the temperature of working environment and air pressure are constant as far as possible; (4) before measurement, carry out instrument calibration and fully preheating; (5) measurand has enough spaces unrestricted with what guarantee to measure around.
2, largescale curved workpiece profile line measuring method
If largescale curved workpiece has design data, can be directly under design coordinate system scanning obtain measurement data, will reduce the error of dataswitching and be convenient to the comparison of data.In addition, for largescale curved workpiece, laser tracker can not have been surveyed data entirety a position, need to carry out multistation measurement, and the laying at reference mark and measurement are exactly a necessity and important work like this.
General using laser tracker measuring system is carried out the measurement of largescale curved workpiece profile line, can be divided into following steps (as shown in Figure 1): (1) coordinate system mark is established and measured; (2) control points layout and measurement; (3) outline line position mark and collection; (4) crosssectional data aftertreatment.Wherein in (2), the measurement at reference mark is mutually reported to the leadship after accomplishing a task and is carried out with (3), the method for taking control limit, limit to gather.
3, coordinate system mark is established and is measured
The reference measurement coordinate system of selected workpiece for measurement.The design coordinate of as far as possible selecting largescale curved workpiece is reference measurement coordinate system, and preferably makes a certain axle (as Z axis) of this reference measurement coordinate system perpendicular to outline line (namely cross section profile marking line place plane).To design coordinate system as reference measurement coordinate system, be for the crosssectional data finally obtaining and design data are compared, the convenient measuring accuracy of evaluating.But in fact, be not limited in the selection of design coordinate system.
In order to determine reference measurement coordinate system, and also carry out coordinate conversion in order to facilitate between reference measurement coordinate system and the system coordinate system of measuring system, need first the surperficial of workpiece for measurement or near select at least three reference points.To be referred to as again unique point for the reference point of tokenbased locating tab assembly coordinate system herein.The principle that unique point mark is established is: the design coordinate of (1) unique point can be determined; (2) be the precision that guarantees the coordinate conversion of reference measurement coordinate system and system coordinate system, the number of unique point can not be less than 4; (3) unique point can not be located on the same line; (4) on a survey station, laser tracker can observe all unique points simultaneously; (5) common unique point is positioned at the surface of workpiece for measurement.
In the time that unique point is observed, what obtain due to laser tracker is gauge head centre coordinate but not unique point coordinate, therefore also needs the data that scanning is obtained to carry out Proberadius Compensation in Reserve.And the compensation process of this gauge head radius both can have been selected Proberadius Compensation in Reserve method of the present invention, also can select method in prior art.As adopt fitting process or penalty method to measure.Fitting process is the extension rod utilizing with prong, and makes needle point be positioned at unique point, and laser tracker scanning is positioned at the rotary motion trace at gauge head center, extension rod top, then obtains the coordinate of unique point by the method for the matching centre of sphere.Also can use some other approximating method, as fit Plane, the principle intersecting at a point by three faces is carried out acquisition point coordinate etc.Penalty method need to be by specialshaped base, base is positioned near unique point, unique point is determined with the position relative fixing and mutual spatial relationship (as distance) at gauge head center, obtained unique point coordinate by the method for calculating compensation space relation.When concrete actual measurement, can select according to principle easily the measuring method of unique point.
The unique point coordinate obtaining through laser tracker is the system coordinate system take laser tracker center as true origin, can all be transformed into and design in coordinate system obtain all measurement data in system coordinate system according to the coordinate in coordinate system in design of unique point, thereby realize the contrast of curved surface profile measurement data and design data.It is poor that coordinate conversion error can not be greater than limit, obtain the outline data of submillimeter level, and its limit difference should be less than 0.5mm.
4, control points layout and measurement
For the less workpiece of scale, only need to determine that a system coordinate system is just passable.Now, laser tracker can complete the measurement of the profile marking line all to surface of the work in said system coordinate system, and these measurement data can all be converted in reference measurement coordinate system through coordinate transform.
But for largescale workpiece, only set a system coordinate system often inadequate.Therefore, need near workpiece, select multiple suitable system coordinate systems, multidrop is measured.Multidrop measurement refers to when the measurement target to being fixed on somewhere is measured, laser tracker is only placed on to a measuring position and can not completes surveying work, need to be by mobile laser tracker (or arranging many laser trackers), respectively measurement target is measured in different positions, the data that finally each station recorded forward in the same coordinate system to be unified to process.Abovementioned multiple measuring position is corresponding multiple system coordinate systems just.
In order to guarantee the precision of the coordinate conversion between multiple system coordinate systems, also need to be near of workpiece for measurement or surperficial selected at least three reference points.Again the reference point between adjacent two system coordinate systems is called to reference mark herein.The laying principle at reference mark is: (1) all reference mark should be evenly distributed on the surrounding of workpiece for measurement; (2) for adjacent two survey stations (system coordinate system), must observe in theory 3 identical reference mark, but for guarantee to turn station precision preferably observe 4 or more than; (3), at each survey station, need the reference mark of observation also should be evenly distributed on laser tracker around.
The survey station of observational characteristic point is made as to the first survey station (supposing that this first survey station is the first system coordinate system), the system coordinate system of laser tracker is transformed in design coordinate system, and the point coordinate that laser tracker records is like this all the coordinate figure in design coordinate system.Then spot measurement is carried out in the reference mark that can observe, and these reference mark can be at second station (supposing that this is the second system coordinate system adjacent with the first system coordinate system) energy repeated measures.So just realize the coordinate conversion between second system coordinate system and the first system coordinate system.And then second system coordinate system is converted to reference measurement coordinate system.The measurement at all the other each stations is all undertaken by above method.
Although the measuring accuracy of laser tracker is higher, consider the impact of environment, the factor such as artificial, must carry out at least twice independent measurement to each reference mark, get the mean value of measurement data in poor scope, just can carry out the measurement of the next stop.
5, cross section contour mark and data acquisition
According to curve surface of workpiece shape, a series of cross section profile line position need to be planned out, and will on workpiece for measurement, be marked out the vestige of position before measurement.The realtime monitored function of laser tracker system can relatively easily complete the mark of outline line position.Vertical owing to cross section and Z axis being made as, only need observation Z value coordinate.But what at this moment system showed is only the Z coordinate at gauge head center, there is a negligible less deviation with the Z value at place, cross section.In when mark, the rugosity of position vestige should not exceed 1mm, and gauge head skew marking line center is excessive when avoiding surveying.In addition,, on a survey station, all cross section profile line positions within observation scope need be marked out.
Before pair crosssection profile mark line sweep, set every measurement parameter of laser tracker system, wherein for guaranteeing that precision can be 1mm by distance samples set of frequency.When scanning, handheld gauge head keeps sliding with image data continuously along cross section profile marking line.Although laser tracker system has continuous light function, when scanning with continuous light for well.On a survey station, the restriction of visual equipment measuring distance, completes the data acquisition of all cross section profile marking line in observation scope.
For the precision that guarantees to measure, need in measuring process, carry out poor checking.Before instrument turns station, again spot measurement is carried out in more than two of our station reference mark, compare the precise decreasing that whether exists movement and environment change to cause of inspection apparatus with the reference mark data of observing.Stand and complete after control survey and coordinate conversion when instrument turns, last two the outline line multiple scannings that need to cross last scan, compare with scandata, judge whether to exist relatively large deviation.
6, the removal of redundant data in measurement data
Handheld gauge head, in the time that scanning starts and finish, can produce some redundant datas.According to the dot spacing of Z value coordinate and cloud data, threshold value is set can be removed redundant points cloud.
7, the radius compensation of gauge head outline line point cloud mid point P
Utilize gauge head to get a little along the scanning of cross section profile marking line, form gauge head outline line point cloud.The gauge head outline line point cloud that gathers gained is only the coordinate data at gauge head center, obtain the outline line point cloud of curve surface of workpiece, also must carry out the compensation of gauge head radius.
For the compensation of gauge head radius, key is to calculate the Surface Method vector of probe location while measurement.Comparatively ripe algorithm has 3 concyclic methods, microplanar process, least square plane fitting process, Enveloped surface method, curve fitting method etc.Conventionally to determine according to the line face requirement of the systematicness of measuring method, measuring object, measurement data etc. the compensation method of gauge head radius.The surface of general largescale curved body is comparatively complicated, in conjunction with the feature of the handheld gauge head measurement of laser tracker, can adopt the method for least square plane matching.Its principle is in a little field of measuring point P, gathers respectively multiple reference point, utilizes least square fitting to go out best fit plane, vows N with the method for this plane _{p}be similar to and carry out radius compensation as the method vector at a P place.
Ultimate principle of the present invention is at the each increase by least one in the both sides of the workpiece cross section profile marking line sweep trace parallel with cross section profile marking line, and forms at least one left line point cloud and at least one right line point cloud.But generally, at sweep trace of each side increase of cross section profile marking line, be called left line and right line, the distance of left line or right line and cross section profile marking line, depending on curve form, is generally 0.5cm left and right.While carrying out data acquisition in sectional position like this, three cloud datas be will scan, gauge head outline line point cloud, left line point cloud and right line point cloud will be respectively.
Take gauge head outline line cloud data as basis, from left line point cloud and right line point cloud, to extract suitable point respectively, and then form some group, fit Plane also obtains normal, then carries out the compensation of gauge head radius.Particularly, from second point of gauge head outline line cloud data, be extracted in two points that are positioned at its front and back in gauge head outline line point cloud, from left line point cloud and right line point cloud, all extract respectively again two points nearest with this point, with the microplane of 7 somes matching (seeing Fig. 2) including this, carry out the Proberadius Compensation in Reserve of gauge head outline line cloud data.Rudimentary algorithm is as follows:
The general expression of plane equation is as follows:
Ax+By+Cz+D＝0，C≠0，
Be rewritten as:
Note:
:
z＝a _{0}x+a _{1}y+a _{2}
For n (n > 3) point (x _{i}, y _{i}, z _{i}), i=0,1L, n1, carrys out fit Plane equation, and least square method requires:
Minimum, should meet:
That is:
Have:
Substitution P (x _{p}, y _{p}, z _{p}) coordinate of 7 points around, separate abovementioned system of equations, obtain a _{0}, a _{1}, a _{2}, the method vector that has this plane is N _{p}(a _{0}, a _{1},1), and carry out the N of unit _{e}, the coordinate of putting the compensation point P ' of P is: (x, y, z)=(x _{p}, y _{p}, z _{p})rN _{e}, the radius that wherein r is gauge head.
Error about Proberadius Compensation in Reserve is relevant with the surface curvature of gauge head radius and tested curved body, and gauge head radius is less, and curvature is less, and error is also less.
8, cross section projection
Cross section projection is that the radius compensation point P ' of the some P in gauge head outline line point cloud is projected on corresponding cross section.Radius compensation point P ' cross section contour projection in the plane can be determined by the intersection point of three planes, first plane was the fit Plane of P ' point, the method of fit Plane is vowed consistent with the method arrow of the some P place fit Plane in gauge head outline line point cloud, vows having obtained for last minute at instructions therefore cross the method for the fit Plane of some P '; Second plane is to pass through the plane of P ' point and Z axis (or coordinate axis of vertical crosssection); The 3rd is projecting section's (cross section contour place plane) (as shown in Figure 3).
If the coordinate of radius compensation point P ' is P ' (x _{0}, y _{0}, z _{0}), need to project to corresponding cross section z=z _{i}on.The fit Plane equation of crossing this point is as follows:
a _{0}(xx _{0})+a _{1}(yy _{0})(zz _{0})＝0
Second plane is that its equation is as follows by the plane of this point and Z axis:
xy _{0}yx _{0}＝0
The intersection point of three planes is as follows:
Separate this system of equations, obtain a P ' (x _{0}, y _{0}, z _{0}) subpoint P on cross section " (x, y, z).
Embodiment
It is measuring object that the present invention has selected fan blade, and it is the key member of aerogenerator.Pneumatic equipment blades made moulding is special, space angle is complicated, length is large, size is more, demand strict technology.The blade of producing must be inspected by random samples, adopts the method for the invention to complete the cross section contour scanning survey of a certain blade to be measured, and compares with design size.This length of blade is 32.8m, root end face diameter 1.68m.Laser tracker measuring system is selected the T3 of API, and Survey Software is SPatial Analyer.
Fan blade root end face is annular plane, can carry out by laser tracker measuring system the detection of flatness and circularity to this plane.If this plane is XY plane, circle ring center is initial point O, and Z axis forms space righthanded coordinate system (seeing Fig. 4) perpendicular to XY plane.Using abovementioned coordinate system as reference measurement coordinate system, design coordinate system when this coordinate system is also fan blade production.For the direction of X and Yaxis, can produce according to blade time, root leaves to identify and sets up, i.e. orthogonal four the some a of line, b, c, d, these four some design coordinates are known, and the coordinate of ordering as a is (0.84,0,0), can be used as the unique point for tokenbased locating tab assembly coordinate system.In the time that first stop is measured, under system coordinate system, measure abovementioned four unique points, by the coordinate transformation function of laser tracker measuring system, system coordinate system is transformed into design coordinate system.
Control points layout and measurement
In order to complete the entire scan of blade, blade is promoted, the about 0.5m in distance from bottom ground, and fixed blade.(see Fig. 5 a), wherein 5 reference mark are positioned at (seeing Fig. 5 (b)) under blade, between adjacent like this survey station, can have 4 shared reference mark at least around blade, to have laid altogether 12 reference mark.According to the measuring distance of the size of blade and laser tracker, be provided with altogether 5 survey stations and complete data scanning, see Fig. 5 (a).
Cross section contour mark and data acquisition
Due to the complex structure of blade, except uniformlyspaced planning cross section contour according to 1m between 30m 1, change place greatly at curvature of curved surface, as 0.1,4.5,23.7,24.5,25.5,26.5,27.2,28.5, the positions such as 29.7,30.5 have increased the scanning (as shown in Figure 6) of cross section contour, have scanned altogether the cross section contour of 40 positions.The Proberadius Compensation in Reserve method that described in detail above according to the present invention gathers cross section contour data and the scanline data of all positions.
Proberadius Compensation in Reserve and outline line cloud data
Utilize method of the present invention to carry out Proberadius Compensation in Reserve to collected gauge head crosssectional data.The gauge head radius that the T3 laser tracking measurement system of API is selected is 19.05mm.Table 1 has been listed the three line sweep data (gauge head outline line point cloud, left line point cloud and right line point cloud) at 4.5m place, sequence number represents the Position Number of the some P in gauge head outline line point cloud, in gauge head outline line point cloud, scan altogether 2627 points, in table, listed the coordinate data of ten points wherein.Table 2 has been listed corresponding radius compensation data (the cross section contour cloud data namely obtaining through Proberadius Compensation in Reserve).Meanwhile, according to cross section mentioned above projecting method, the data projection after compensation is arrived to standard planning position, therefore be also listed as the projected position data that after 4.5m place Proberadius Compensation in Reserve in table 2.
The scandata (unit: mm) of table 1 gauge head outline line point cloud, left line point cloud and right line point cloud
Table 2 Proberadius Compensation in Reserve and data for projection (unit: mm)
Data comparison and analysis
In order to check the correctness of the method for the invention, final measurement data and design data are contrasted.Method is that the section line of the some cloud of the cross section contour finally obtaining and design data has been carried out apart from calculating.Can find out that from this table maximum is just apart from being 1.438, maximum negative distance value is2.735, is 0.159 apart from the average of difference, and variance yields is 0.307, illustrates that this blade production is qualified, thereby has verified the correctness of the method for the invention.
Although embodiment of the present invention are open as above, but it is not restricted to listed utilization in instructions and embodiment, it can be applied to various applicable the field of the invention completely, for those skilled in the art, can easily realize other modification, therefore do not deviating under the universal that claim and equivalency range limit, the present invention is not limited to specific details and illustrates here and the legend of describing.
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