CN103542982A - System for measuring rotational inertia of large structural body - Google Patents

Abstract

The invention discloses a system for measuring the rotational inertia of a large structural body. The system comprises a bottom board, and the bottom board is provided with a y-directional measurement system or an x-directional measurement system. The system can measure the y-directional rotational inertia and the x-directional rotational inertia of a measured product in a separated mode, and the measurement in the x direction and the measurement in the y direction are finished on the premise of not turning over the measured product by the same test board; the rolling supporting mode that a bearing assembly and a roller bearing are combined is adopted, the damping influence of the system is reduced greatly, and the measurement precision of the system is improved. The system is high in universality, can measure large structural bodies of different shapes and different standards, and is high in measurement precision, wide in measurement range, low in cost and convenient to maintain.

Description

A kind of large structure Measurement System of " Moment of Inertia

Technical field

The present invention relates to mechanical hook-up and transportation technology field, particularly a kind of large structure Measurement System of " Moment of Inertia.

Background technology

The tolerance of inertia when moment of inertia is Rigid Body in Rotation With, every problem that relates to rotational power, moment of inertia is focus measurement parameter.In national defense industry, various guided missiles, unmanned vehicle and under water unmanned vehicles all need to measure its utmost point, equator moment of inertia, in order to determine their initial disturbance and the stability of advancing;

In existing list of references and patent about rotation inerttia, the ultimate principle of following is: utilize flexible member to form oscillatory system, by system oscillation frequency, calculate moment of inertia.Main measuring method is: compound pendulum, Inertia Based on Torsion Pendulum Method, three-line pendulum method, single line arrangement and Constructional Elements Using Falling Methods etc.But owing to being subject to the restriction of Design of Mechanical Structure and testee shape difference, less for the measuring method of large structure.The design > > of document < < large revolving body Measurement System of " Moment of Inertia has provided a kind of comparatively advanced measuring system for large-sized object, but this system fixed mechanism adopts ball to support, be a contact, when measured piece quality is larger, system damping is very big, in addition, when measured piece surface is comparatively coarse, point contact can cause larger damping fluctuation, all can bring very large impact to the measuring precision.Meanwhile, this system is, large revolving body that shape single even for mass distribution only, and, mass distribution uneven product large for shape difference, this system cannot be measured.For being shaped as the guided missile, unmanned aerial vehicle of non-single solid of revolution, the rotation inerttia of the object such as unmanned vehicles under water, this system is no longer applicable.

Summary of the invention

Technical matters to be solved by this invention is, for prior art deficiency, to provide a kind of simple in structure, easy to operate, the large structure Measurement System of " Moment of Inertia that measuring accuracy is high, applied widely.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of large structure Measurement System of " Moment of Inertia, comprise base plate, and its architectural feature is:

When measuring large structure y to moment of inertia, on described base plate, y is installed to measuring system; Described y comprises that to measuring system the tested structure that is used to being fixed on base plate provides y to the y of torsional moment to rotating cylinder assembly, described y is fixed with support plate to rotating cylinder assembly upper end, two closed slides on described support plate, have been horizontally disposed with, an above slide block that can slide along described guide rail is installed on every guide rail, y on two closed slide relative positions is one group to measuring slide block, and every group of y is fixed with one for the fixed mechanism of fixing tested structure to measuring on slide block; On described support plate, be provided with for measuring described y to the grating scale of measuring slide block sliding distance; Described support plate lower surface is fixed with y to measuring photometer head; On described base plate, be fixed with described y to measuring the supporting y of photometer head to measuring photoreceptor;

When measuring large structure x to moment of inertia, on described base plate, x is installed to measuring system; Described x comprises that to measuring system two x that are set in parallel in described base plate one end are to measuring horizontal guide rail; On horizontal guide rail, be respectively provided with more than one can be along described x to measuring x that horizontal guide rail slides to measurement slide block to measuring for described two x; Two x are one group to the x measuring on horizontal guide rail relative position to measuring slide block, and every group of x is fixed with a bracing frame to measuring on slide block; Support frame as described above top provides x to be fixedly connected with to reversing assembly one end to the x of torsional moment with being used to described tested structure; Described x is connected with described tested structure one end to reversing the assembly other end; Described x is fixed with x to measuring photometer head to reversing assembly lower surface, and described x is fixed with described x to measuring the supporting x of photometer head to measuring photoreceptor on the base plate of measurement horizontal guide rail one end.

Described support plate lower surface offers ring groove; Described y comprises that to rotating cylinder assembly the fixing y vertically arranging is to rotating cylinder, and described y is less than described y to rotating cylinder upper end diameter to rotating cylinder bottom diameter, and described y embeds described ring groove to rotating cylinder upper end, and described y is connected with described base plate by abutment ring to rotating cylinder bottom; Described y is vertically provided with y to torsion bar in rotating cylinder, and described y is fixedly connected with the support plate lower surface in described ring groove to torsion bar upper end, and described y is fixedly connected with described base plate through described abutment ring to torsion bar lower end; Described y has bottom to be fixed on the protection cylinder on described base plate to rotating cylinder overcoat; Described protection cylinder upper end, y are respectively equipped with groove and boss to rotating cylinder upper end relative position, are provided with y to measuring roller bearing in described groove, and described y is to measuring roller bearing and the laminating of described boss upper surface; Described y is placed on the thrust ball bearing on described abutment ring to the concave station forming between rotating cylinder to the y in rotating cylinder bottom smaller-diameter portion and this part; Described protection cylinder bottom inner bulge, this bossing and described Contact of Thrust Ball Bearing.

The x that described x comprises an end opening to torsion assembly is to stationary magazine creel, x to rotating cylinder; Described x is fixedly connected with support frame as described above top by contiguous block to stationary magazine creel; To stationary magazine creel, the not openend bottom surface inwall away from tested structure is fixedly connected with to torsion bar one end with x described x; Described x is less than other end diameter to rotating cylinder one end diameter; Described x is enclosed within described x to rotating cylinder diameter less one end on by x to roller bearing near one end of tested structure to stationary magazine creel; Described x is also fixing to the less one end of rotating cylinder diameter through described x near one end of tested structure to torsion bar; Described x is fixedly connected with described tested structure by abutment ring to one end of stationary magazine creel away from described x to rotating cylinder.

Described y comprises two fixed mechanisms to measuring system; Described fixed mechanism comprises set collar, fixed ring inwall contacts with rotating snap ring outer wall by a plurality of bearing assemblies of uniformly-spaced arranging, and described rotation snap ring can rotate centered by passing the described rotation snap ring center of circle and the axle vertical with described rotation snap ring place plane; Fixed ring, to rotate snap ring concentric; Described rotation snap ring internal diameter mates with described tested structure external diameter size; Described outer set collar is fixedly connected with to measuring slide block with described y by base.

Compared with prior art, the beneficial effect that the present invention has is: the present invention is simple in structure, easy to operate, is applicable to the measurement of large structure moment of inertia; Test product x is to separating and carry out to the measurement of moment of inertia with y, realizes and at same test board, completes the measurement of x to, y to both direction under to measured piece upset prerequisite; The supporting way that the present invention adopts bearing assembly to combine with roller bearing, has greatly reduced system damping impact, has improved the measuring precision; Highly versatile of the present invention, can realize difform large product is measured to rotating cylinder by changing different fixed mechanisms and x; And when product is measured, only need the location that regulates corresponding fastening bolt just can realize product with fixing, easy to operate, simple; The present invention has abandoned the complicated automation equipment that prior art is made earnest efforts, and has greatly reduced cost of equipment; Photometer head and photoreceptor convenient disassembly, can independently demarcate; Measuring accuracy of the present invention is high, test specification is wide, equipment cost is low, easy to maintenance; The present invention can be widely used in scientific research, the production fields such as space flight, aviation, navigation, weapons, machinery, motor and biomechanics, has great practical value.

Accompanying drawing explanation

Fig. 1 is one embodiment of the invention structural representation;

Fig. 2 is that one embodiment of the invention y is to rotating cylinder modular construction schematic diagram;

Fig. 3 is that one embodiment of the invention x is to reversing modular construction schematic diagram;

Fig. 4 is one embodiment of the invention fixed sturcture schematic diagram.

Embodiment

As shown in Figure 1, one embodiment of the invention comprises base plate 11, when when measuring large structure y to moment of inertia, on described base plate 11, y is installed to measuring system; Described y comprises that to measuring system the tested structure 5 that is used to being fixed on base plate 11 provides y to the y of torsional moment to rotating cylinder assembly, described y is fixed with support plate 9 to rotating cylinder assembly upper end, two closed slides 6 on described support plate 9, have been horizontally disposed with, an above slide block 7 that can slide along described guide rail 6 is installed on every guide rail 6, y on two closed slide 6 relative positions is one group to measuring slide block 7, and every group of y is fixed with one for the fixed mechanism of fixing tested structure 5 to measuring on slide block 7; On described support plate 9, be provided with for measuring described y to the grating scale of measuring slide block 7 sliding distances; Described support plate 9 lower surfaces are fixed with y to measuring photometer head 8; On described base plate 11, be fixed with described y to measuring the supporting y of photometer head to measuring photoreceptor 10; When measuring large structure x to moment of inertia, on described base plate 11, x is installed to measuring system; Described x comprises that to measuring system two x that are set in parallel in described base plate 11 one end are to measuring horizontal guide rail 15; On horizontal guide rail 15, be respectively provided with more than one can be along described x to measuring x that horizontal guide rail 15 slides to measurement slide block 14 to measuring for described two x; Two x are one group to the x measuring on horizontal guide rail 15 relative positions to measuring slide block 14, and every group of x is fixed with a bracing frame 1 to measuring on slide block 14; Support frame as described above 1 top provides x to be fixedly connected with to reversing assembly one end to the x of torsional moment with being used to described tested structure 5; Described x is connected with described tested structure 5 one end to reversing the assembly other end; Described x is fixed with x to measuring photometer head 2 to reversing assembly lower surface, and described x is fixed with described x to measuring the supporting x of photometer head 2 to measuring photoreceptor 13 on the base plate 11 of measurement horizontal guide rail 15 one end.

As Fig. 2, support plate 9 lower surfaces offer ring groove; Described y comprises that to rotating cylinder assembly the fixing y vertically arranging is to rotating cylinder 18, described y is less than described y to rotating cylinder 18 upper end diameter to rotating cylinder 18 bottom diameters, described y embeds described ring groove to rotating cylinder 18 upper ends, and described y is connected with described base plate 11 by abutment ring 20 to rotating cylinder 18 bottoms; Described y is to the interior y that is vertically provided with of rotating cylinder 18 to torsion bar 19, and described y is fixedly connected with support plate 9 lower surfaces in described ring groove to torsion bar 19 upper ends, and described y is fixedly connected with described base plate 11 through described abutment ring 22 to torsion bar 19 lower ends; Described y has bottom to be fixed on the protection cylinder 21 on described base plate 11 to rotating cylinder 18 overcoats; Described protection cylinder 21 upper ends, y are respectively equipped with groove and boss 12 to rotating cylinder 18 upper end relative positions, are provided with y to measuring roller bearing 16 in described groove, and described y is to measuring roller bearing 16 and described boss 12 upper surface laminatings; Described y is placed on the thrust ball bearing 22 on described abutment ring 22 to the concave station forming between rotating cylinder 18 to the y in rotating cylinder 18 bottom smaller-diameter portion and this part; Described protection cylinder 21 bottom inner bulge, this bossing contacts with described thrust ball bearing 22.

As Fig. 3, the x that x comprises to torsion assembly the end opening being fixedly connected with support frame as described above 1 top is to stationary magazine creel 24, x to rotating cylinder 26; Described x is fixedly connected with support frame as described above 1 top by contiguous block 29 to stationary magazine creel 24; To stationary magazine creel 24, the not openend bottom surface inwall away from tested structure 5 is fixedly connected with to torsion bar 23 one end with x described x; Described x is less than other end diameter to rotating cylinder 26 one end diameters; Described x is enclosed within described x to rotating cylinder 26 diameters less one end on by x to roller bearing 25 near one end of tested structure 5 to stationary magazine creel 24; Described x is also fixing to rotating cylinder 26 less one end of diameter through described x near one end of tested structure 5 to torsion bar 23; Described x is fixedly connected with described tested structure 5 by abutment ring 27 to one end of stationary magazine creel 24 away from described x to rotating cylinder 26.

As Fig. 4, y comprises two fixed mechanisms to measuring system; Described fixed mechanism comprises outer set collar 32, described outer set collar 32 inwalls contact with rotating snap ring 33 outer walls by a plurality of bearing assemblies 31 of uniformly-spaced arranging, and described rotation snap ring 33 can rotate centered by passing described rotation snap ring 33 centers of circle and the axle vertical with described rotation snap ring 33 place planes; Described outer set collar 32, to rotate snap ring 33 concentric; Described rotation snap ring 33 internal diameters mate with described tested structure 5 external diameter sizes; Described outer set collar 32 is fixedly connected with to measuring slide block 7 with described y by base 34.Rotate snap ring 33 outer walls and offered groove, the bearing 35 on bearing assembly 31 contacts with groove, rotates snap ring and can rotate relative to bearing 35.

Tested structure 5 is positioned over and rotates in snap ring 33, adjusts fastening bolt 30, and itself and tested structure 5 are posted and fixed; By changing bearing assembly 31 and rotating snap ring 33 to adapt to the tested structure of different size size, along guide rail 6, move y to measuring slide block slide block 7, thereby change the position of tested structure 5 on support plate 9.

Y is spirally connected and is fixed on support plate 9 lower surface centers to torsion bar 19, and y becomes cross key to torsion bar 19 lower ends, inserts the cross recess of lower shoe 11 middle parts.During measurement, y is limited by cross recessed to torsion bar 19, provides and rocks moment of torsion, and y supports support plate 9 to rotating cylinder 18 and rotates around y axle.

X is the Step Shaft in inner threaded hole to the less one end of rotating cylinder 26 diameters, x is to torsion bar 23 two ends machining screw, roller bearing 25 inner rings are enclosed within x on rotating cylinder Step Shaft, and roller bearing 25 outer rings are arranged on x to stationary magazine creel 24 on the step near tested structure 5 one end; X establishes a tapped through hole to stationary magazine creel 24 away from tested structure 5 one end, be spirally connected and fix by nut to torsion bar 23 with x, by change, change x to rotating cylinder 26 and adapter ring 28, and change x to measure slide block at x to the position of measuring on horizontal guide rail, adapt to the tested structural member of different size specification.

Utilize apparatus of the present invention to carry out the process of rotation inerttia as follows:

Reliable for guaranteeing measured piece measurement result, need to prepare a standard component, for regular shape, the equally distributed standard component of quality, can calculate fine determine its centroid position and moment of inertia by theory, the total moment of inertia of the unloaded moment of inertia of system, standard component moment of inertia, system and measured piece of setting up departments is respectively: I ₀, I _b, I _d2; The total total damped oscillation frequency of damped oscillation frequency, system and measured piece of unloaded damped oscillation frequency, system and standard component is respectively: ω _d0, ω _d1, ω _d2, system is freely rocked oscillation equation and be can be described as:

$I_0\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&theta;}}+c\stackrel{\&CenterDot;}{\mathrm{\&theta;}}+\mathrm{k\&theta;}=0$

In formula: θ is for rocking angle; C is ratio of damping; K is torsion bar stiffness coefficient.

Order $\frac{c}{I_0}=2\mathrm{\&zeta;},\frac{k}{I_0}={{\mathrm{\&omega;}}_{n0}}^2$

In formula: ω _n0for system frequency, ζ is system damping.

Can obtain:

${\mathrm{\&omega;}}_{d0}=\sqrt{{{\mathrm{\&omega;}}_{n0}}^2-{\mathrm{\&xi;}}^2}$

Above formula is system damping oscillation frequency equation.A kind of large structure Measurement System of " Moment of Inertia of the present invention rocks as damped oscillation, support rotating assembly adopts bearing assembly and roller bearing combination, greatly reduced system damping impact, on damping impact of the present invention, analyze known, damping impact of the present invention is little, system testing precision is high, and derivation can obtain:

$I_0=\frac{I_b}{{\left(\frac{{\mathrm{\&omega;}}_{d0}}{{\mathrm{\&omega;}}_{d1}}\right)}^2-1}$

$I=I_b\frac{{\left(\frac{{\mathrm{\&omega;}}_{d0}}{{\mathrm{\&omega;}}_{d2}}\right)}^2-1}{{\left(\frac{{\mathrm{\&omega;}}_{d0}}{{\mathrm{\&omega;}}_{d1}}\right)}^2-1}$

In above formula, I is measured piece moment of inertia.

Standard component measuring process is:

(1): frock is prepared, guide rail 6 is coordinated and is fixed on support plate 9 to measuring slide block 7 with y, fixed mechanism base and y are spirally connected fixing to measurement slide block 7, adjust relative position, and bearing assembly is installed in outer set collar; Y is assembled and is guaranteed the alignment of parts according to assembly relation to rotating cylinder assembly; Y is fixedly connected with base plate with upper bearing plate respectively to rotating cylinder assembly; Install y to measuring photometer head and y to measuring photoreceptor;

(2) standard component is installed, and standard component is put into rotation snap ring, then rotation snap ring is positioned on bearing assembly together with standard component; Adjust fastening bolt, bolt contact with standard component, the relative position of change fastening bolt, makes standard component symmetry, the stable support plate that is fixed on; Demarcate standard component barycenter, moving slider, makes barycenter overlap with O point;

(3) demarcate y to measure photometer head with y to measurement photoreceptor, controller, industrial computer are ready;

(4) standard component is turned an angle and then discharged around y axle, y records related data and passes to industrial computer to measuring photoreceptor to measuring photometer head and y, and industrial computer backstage is processed and shown that its y is to damped oscillation frequencies omega _b1; For guarantee obtaining measurement data comparatively accurately, the anglec of rotation of standard component should be greater than 5 °, guarantees that y does not rupture to torsion bar simultaneously, the concrete anglec of rotation depending on standard component size and y to torsion bar intensity;

(5) x is assembled to reversing assembly, x is inserted in from standard component head to rotating cylinder, regulates set bolt, makes x coaxial to rotating cylinder and standard component;

(6) demarcate x to photoelectric sensor, and standard component is rotated to an angle and then discharged around x axle, photosensors record related data is also passed to industrial computer, and industrial computer backstage is processed and shown that its x is to damped oscillation frequencies omega _d1;

(7) standard component is taken off, y when measuring system is unloaded is to damped oscillation frequencies omega _b0, x is to damped oscillation frequencies omega _d0; And above data measured is stored in to industrial computer, measurement later is directly called.

When tested structure is unsymmetric structure, fastening bolt is asymmetric adjustment along circumference, and fastening bolt can bring error to system rotation inerttia; But it is minimum that fastening bolt mass distribution causes the moment of inertia value of the relative measured piece of amount of moment of inertia variation, so its impact can be ignored.Object that cannot be definite for centroid position, adopts shift method to measure, and utilizes parallel shafts shifting principle to have:

I _y+mr ²=I ₁

In formula, I _yobject is about the moment of inertia of mass axis, and r is the vertical range of rotating shaft and mass axis, I ₁for the moment of inertia of object about rotating shaft.

Tested structure rotation inerttia step is as follows:.

(1) tested structure is installed, and with reference to abovementioned steps one, step 2, step 3, step 5 and step 6, tested structure is installed on to measuring table, and has demarcated photoelectric sensor (being photometer head and photoreceptor);

(2) structure system for winding x axle is rotated to an angle, record the total x of system and structure to oscillation frequency ω _x1; Adjust fastening bolt, change the position of tested construction yoz plane, record the position of any two points, require these 2 with 3 of initial points not point-blank, measure its corresponding oscillation frequency, by calculating, can determine that structure crosses the x axle of barycenter, and obtain structure around the moment of inertia I of this axle _x;

(3) remove x axle and reverse assembly, adjust tested structure, make system y axle parallel with the structure y axle of definition, and the system x axle x axle definite with step 2 overlapped, tested structure is rotated to an angle around y axle, record its oscillation frequency ω _y1; Adjust fastening bolt, along x axle, change tested structure position, record apart from x ₁, by abovementioned steps, record oscillation frequency ω _y2; By calculating, can determine that structure crosses the y axle of barycenter, and obtain structure around the moment of inertia I of this axle _y;

(4) adjust structure, make system y axle and step 3 determine that y axle overlaps, will rotate snap ring around x axle half-twist, by abovementioned steps, can record structure around z axle moment of inertia I _z.

Claims (4)

1. a large structure Measurement System of " Moment of Inertia, comprises base plate (11), it is characterized in that:

When when measuring large structure y to moment of inertia, described base plate is provided with y to measuring system on (11), described y comprises that to measuring system the tested structure (5) that is used to being fixed on base plate (11) provides y to the y of torsional moment to rotating cylinder assembly, described y is fixed with support plate (9) to rotating cylinder assembly upper end, two closed slides (6) on described support plate (9), have been horizontally disposed with, an above slide block (7) that can slide along described guide rail (6) is installed on every guide rail (6), y on two closed slides (6) relative position is one group to measuring slide block (7), every group of y is fixed with one for the fixed mechanism of fixing tested structure (5) to measuring on slide block (7), on described support plate (9), be provided with for measuring described y to the grating scale of measuring slide block (7) sliding distance, described support plate (9) lower surface is fixed with y to measuring photometer head (8), on described base plate (11), be fixed with described y to measuring the supporting y of photometer head to measuring photoreceptor (10),

When measuring large structure x to moment of inertia, described base plate is provided with x to measuring system on (11); Described x comprises that to measuring system two x that are set in parallel in described base plate (11) one end are to measuring horizontal guide rail (15); On horizontal guide rail (15), be respectively provided with more than one can be along described x to measuring x that horizontal guide rail (15) slides to measurement slide block (14) to measuring for described two x; Two x are one group to the x measuring on horizontal guide rail (15) relative position to measuring slide block (14), and every group of x is fixed with a bracing frame (1) to measuring on slide block (14); Support frame as described above (1) top provides x to be fixedly connected with to reversing assembly one end to the x of torsional moment with being used to described tested structure (5); Described x is connected with described tested structure (5) one end to reversing the assembly other end; Described x is fixed with x to measuring photometer head (2) to reversing assembly lower surface, and described x is fixed with described x to measuring the supporting x of photometer head (2) to measuring photoreceptor (13) on the base plate (11) of measurement horizontal guide rail (15) one end.

2. large structure Measurement System of " Moment of Inertia according to claim 1, is characterized in that, described support plate (9) lower surface offers ring groove; Described y comprises that to rotating cylinder assembly the fixing y vertically arranging is to rotating cylinder (18), described y is less than described y to rotating cylinder (18) upper end diameter to rotating cylinder (18) bottom diameter, described y embeds described ring groove to rotating cylinder (18) upper end, and described y is connected with described base plate (11) by abutment ring (20) to rotating cylinder (18) bottom; Described y is vertically provided with y to torsion bar (19) in rotating cylinder (18), described y is fixedly connected with support plate (9) lower surface in described ring groove to torsion bar (19) upper end, and described y is fixedly connected with described base plate (11) through described abutment ring (22) to torsion bar (19) lower end; Described y has bottom to be fixed on the protection cylinder (21) on described base plate (11) to rotating cylinder (18) overcoat; Described protection cylinder (21) upper end, y are respectively equipped with groove and boss (12) to rotating cylinder (18) upper end relative position, in described groove, be provided with y to measuring roller bearing (16), and described y is to measuring roller bearing (16) and the laminating of described boss (12) upper surface; Described y is placed on the thrust ball bearing (22) on described abutment ring (22) to the concave station forming between rotating cylinder (18) to the y in rotating cylinder (18) bottom smaller-diameter portion and this part; Described protection cylinder (21) bottom inner bulge, this bossing contacts with described thrust ball bearing (22).

3. large structure Measurement System of " Moment of Inertia according to claim 1, is characterized in that, the x that described x comprises an end opening to torsion assembly is to stationary magazine creel (24), x to rotating cylinder (26); Described x is fixedly connected with support frame as described above (1) top by contiguous block (29) to stationary magazine creel (24); To stationary magazine creel (24), the not openend bottom surface inwall away from tested structure (5) is fixedly connected with to torsion bar (23) one end with x described x; Described x is less than other end diameter to rotating cylinder (26) one end diameter; Described x is enclosed within described x to rotating cylinder (26) diameter less one end on by x to roller bearing (25) to one end of the close tested structure (5) of stationary magazine creel (24); Described x is also fixing to the less one end of rotating cylinder (26) diameter through described x near one end of tested structure (5) to torsion bar (23); Described x is fixedly connected with described tested structure (5) by abutment ring (27) to one end of stationary magazine creel (24) away from described x to rotating cylinder (26).

4. large structure Measurement System of " Moment of Inertia according to claim 1 and 2, is characterized in that, described y comprises two fixed mechanisms to measuring system; Described fixed mechanism comprises outer set collar (32), described outer set collar (32) inwall contacts with rotating snap ring (33) outer wall by a plurality of bearing assemblies (31) of uniformly-spaced arranging, and described rotation snap ring (33) can rotate centered by passing described rotation snap ring (33) center of circle and the axle vertical with described rotation snap ring (33) place plane; Described outer set collar (32), rotation snap ring (33) are with one heart; Described rotation snap ring (33) internal diameter mates with described tested structure (5) external diameter size; Described outer set collar (32) is fixedly connected with to measuring slide block (7) with described y by base (34).

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