CN101081481A - Method of quick measuring positioning accuracy of Numerically controlled revolving dial measuring mechanism - Google Patents

Abstract

The present invention is fast method of measuring the location precision of measurement mechanism of numerically controlled rotary table. The method includes sampling n times with the computer while the numerically controlled rotary table rotates for one turn, sampling the displayed angle values of the circular grating in the measurement mechanism and the displayed length values of two pen type length gauges dynamically or statically, calculating the offset quantities between the main shaft gyration center in the measurement mechanism and gyration center in the numerically controlled rotary table by means of least square method, establishing mathematic model based on the structure of the measurement mechanism, and calculating the location precision of different points and the total location precision of the numerically controlled rotary table.

Description

The method of quick measuring positioning accuracy of Numerically controlled revolving dial measuring mechanism

Technical field:

The measuring method of the positioning accuracy of the measurement mechanism on the rotary table of the present invention and Digit Control Machine Tool is relevant.

Background technology:

The NC rotary table positioning accuracy dynamically, during rapid static surveying, because measuring mechanism is made the angular surveying reference element with the circle grating, have only when the centre of gyration of justifying grating is concentric with the centre of gyration of NC rotary table, the angle that the circle grating shows is only the angle that NC rotary table turns over.Yet when measuring mechanism was installed on the NC rotary table, the centre of gyration that can not reach round grating was just in time concentric with the centre of gyration of NC rotary table.Therefore, the angle that must turn over the NC rotary table that the circle grating shows is revised.

Summary of the invention:

The method that the purpose of this invention is to provide the quick measuring positioning accuracy of Numerically controlled revolving dial measuring mechanism that angle that a kind of NC rotary table that the circle grating is shown turns over revises.

The present invention is achieved in that

The method of quick measuring positioning accuracy of Numerically controlled revolving dial measuring mechanism of the present invention, the main shaft 10 and the base plate 1 of measuring mechanism are connected, positioner is positioned main shaft 10 in the hole at NC rotary table center, main shaft 10 is connected with the groove ring of circle grating, circle grating seat and axle sleeve and first connecting plate 15 are connected, first connecting plate 15 is connected with optical axis 14, second connecting plate 17 is connected with chuck 20, two pen type length gauges 32 are connected with first or second connecting plate, its axis becomes 90 ° of angles by the centre of gyration of main shaft 10, the axis of a pen type length gauge and the axis of optical axis are in same vertical guide, the gauge head of pen type length gauge closely contacts with the internal face M of the gage button that second connecting plate or first connecting plate are connected, optical axis connects between 17 two needle rollers or the straight pin 49 and gapped with it second, and its measuring process is as follows:

(1) when the driven by servomotor NC rotary table goes to the datum mark of NC rotary table, from datum mark, the sampling number n that the servomotor encoder rotates a circle according to the default NC rotary table of computer, computer dynamic or the static shaft angle α that the circle grating is turned over _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark,

(2) with the x of pen type length gauge _iValue and corresponding i value obtain the directions X eccentric amount e with polynomial least square fitting _Xi, i=0 wherein, 1,2,3 ... n-1,

(3) with the y of pen type length gauge _iValue and corresponding i value obtain Y direction eccentric amount e with polynomial least square fitting _Yi, i=0 wherein, 1,2,3 ... n-1,

(4) the difference Δ of calculating circle grating corner and NC rotary table actual rotational angle _i,

${\mathrm{\Δ}}_i={\mathrm{tg}}^{-1}\frac{e_{\mathrm{xi}}}{r+e_{\mathrm{yi}}},$

R is the designed distance of circle grating oscillation center,

(5) calculate NC rotary table actual rotational angle β _i,

β _i＝α _i+Δ _i，

α _iBe circle grating corner,

(6) the corner deviation δ of calculating NC rotary table _i,

${\mathrm{\δ}}_i={\mathrm{\β}}_i-\frac{360\×60\×{60}^{\′\′}}{n}\×n_i,$

n _iBe the arbitrary positive integer among the 1-n,

(7) ask δ _iMaximum δ _MaxWith minimum of a value δ _Min,

(8) the positioning accuracy δ of calculating NC rotary table,

δ＝δ _max-δ _min。

In the step (1), from datum mark, the servomotor encoder sends signal according to the sampling number n that the default NC rotary table of computer rotates a circle by the equal angles spacing, the shaft angle α that computer turns over the circle grating automatically _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark.

In the step (1), from datum mark, the servomotor encoder is according to the sampling number n that the default NC rotary table of computer rotates a circle, and stops after turning over an equidistant angle, and computer is by manually or the shaft angle α that automatically the circle grating is turned over _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark.

The measuring mechanism that method of the present invention is utilized simple in structure, low cost of manufacture, easy to use, image data easily and fast, computer is handled according to image data, can quick and precisely obtain NC rotary table, the positioning accuracy of corresponding each point and general orientation precision from datum mark.

Description of drawings:

Fig. 1 is the structure chart of the used measuring mechanism of the present invention.

Fig. 2 is the E-E cutaway view of Fig. 1.

Fig. 3 is that the A of Fig. 1 is to partial view.

Fig. 4 is that the W of Fig. 3 is to partial view.

Fig. 5 is the C-C partial sectional view of Fig. 1.

Fig. 6 is the D-D partial sectional view of Fig. 1.

Fig. 7 is principle of the invention figure.

Fig. 8 is a dynamic acquisition data flowchart of the present invention.

Fig. 9 is dynamic static data flow process figure of the present invention.

Figure 10 is flow chart of data processing figure of the present invention.

The specific embodiment:

Measurement mechanism of the present invention has four kinds of structures, with embodiment 1 structure it is described.

Embodiment 1:

Round grating with band built-in bearing and stator shaft coupling is made the angular surveying reference element, and the misalignment measurement length gauge moves by offset, as Fig. 1, and 2,3,4,5, shown in 6.

Angular surveying is by base plate 1, axillare 4, gripper shoe 6, connecting ring 8, main shaft 10, positioning sleeve 31, locating pin 32 and circle grating 9, thrust ball bearing 29 compositions such as grade.Circle grating 9 usefulness screws 7 tighten together with gripper shoe 6, connecting ring 8 usefulness screws 27 tighten together with gripper shoe 6, the main shaft 10 usefulness collar nuts 11 and the first circle grating 9 are connected, the part of thrust ball bearing 29 is packed on the shaft shoulder of main shaft 10, again axillare 4 is contained on the main shaft 10, and axillare 4 and gripper shoe 6 are connected with screw 5, the part of thrust ball bearing 29 is contained on the main shaft 10, positioning sleeve 31 is pressed in the main shaft 10, with screw 30 base plate 1 and main shaft 10 are reinforced, this has just formed the angular surveying part.Locating pin 32 is used as the location of instrument on workbench 33 when measuring according to the hole dimension manufacturing at NC rotary table center.

Misalignment measurement is by back-up block 13, optical axis 14, the first connecting plates 15, the second connecting plates 17, connecting rod 19, limited post 22, locating pin 24, bearing 36, shifting block 46 and pen type length gauge 37, permanent magnet 48, compositions such as needle roller or quenching straight pin 49.First connecting plate, 15 usefulness screws 25 are fastening with connecting ring 8, after putting into optical axis 14 in two back-up blocks 13, with screw 12 itself and first connecting plate 15 are reinforced, with screw 38 optical axis 14 is clamped in two back-up blocks 13 respectively again, limited post 22 usefulness screws 21 are fastened on first connecting plate 15, after steel ball 23 cements with locating pin 24, be screwed into it in first connecting plate 15 and reinforce, with screw 35 bearing 36 is reinforced after on first connecting plate 15, again two screws 34 of two pen type length gauges, 37 usefulness are fastened in the bearing 36; Be pressed into two needle rollers or quenching straight pin 49 in the shifting block 46, after permanent magnet 48 is cemented on the shifting block 46, the shifting block 46 usefulness screws 47 and second connecting plate 17 are reinforced, the connecting rod 19 usefulness screws 18 and second connecting plate 17 are reinforced, second connecting plate 17 that installs shifting block 46 and connecting rod 19 is placed on first connecting plate 15 and by three locking balls, 23 location, at this moment, optical axis 14 should just in time be between two needle rollers 49 on the shifting block 46, the gauge head of two pen type length gauges 37 closely contacts with the inner hole surface M of second connecting plate 17, and this has just formed the misalignment measurement part.

For attached cable, with screw 41 cable block 40 is fastened on the periphery at cable outlet place of connecting ring 8, the cable of circle grating 9 from cable block 40 along going out, the cable of two pen type length gauges 37 goes out behind cable block 40 from the Kong Shun of first connecting plate 15, and end cap 39 usefulness screws 41 and cable block 40 are fastening and push down the cable of round grating 9 and pen type length gauge 37.Arrive this, measuring mechanism is promptly formed.

For protecting instrument and preventing that dust from entering thrust ball bearing 29, the protective cover 16 usefulness screws 26 and first connecting plate 15 are reinforced, and guard shield 3 usefulness screws 2 are reinforced on base plate 1, are stained with felt collar 28 again on guard shield 3; For ease of the installation of instrument and move, after bearing 42 usefulness screws 44 were reinforced with connecting ring 8, handle 43 usefulness screws 45 and bearing 42 were reinforced.

Points for attention: the round grating 9 of this embodiment is round gratings of band built-in bearing and stator shaft coupling, and the mechanical precision of main shaft 10 and circle grating 9 coupling parts must meet the requirement of round grating 9; During assembling, when thrust ball bearing 29 closely contacted with the shaft shoulder L of main shaft 10, the lower surface F of gripper shoe 6 must be same plane with all plane, place, steel ball lower surface G of thrust ball bearing 29; The periphery J of positioning sleeve 31 and the inner hole surface H of main shaft 10 be interference fits, with the inner hole surface I of base plate 1 be matched in clearance, the periphery Q of locating pin 32 and the inner hole surface P of positioning sleeve 31 are matched in clearance, and the inner hole surface K at the periphery S of locating pin 32 and NC rotary table 33 centers is a matched in clearance; The axis of two pen type length gauges 37 should be by main shaft 10 the centre of gyration, axis should be vertical mutually, and the axis of a pen type length gauge 37 should with the axis of optical axis 14 in same vertical guide; Optical axis 14 is between two needle rollers 49, must be gapped; Cross the inhomogeneous impact that produces of work table rotation in large impact and the measuring process when avoiding NC rotary table to start, it is very important cementing two blocks of permanent magnets 48 on shifting block 46.

The quick measurement of NC rotary table positioning accuracy is achieved in that

(1). kinetic measurement: locating pin 32 is put into the endoporus at NC rotary table 33 centers, measuring mechanism is placed on the table top of NC rotary table, measuring mechanism is positioned on the table top of rotary table with the inner hole surface P of positioning sleeve 31 and the periphery Q of locating pin 32; Behind chuck 20 declines and the clamping connecting rod 19, the chuck 20 that rises again breaks away from the steel ball 23 and second connecting plate 17 on the locating pin 24.The driven by servomotor workbench rotation of NC rotary table, when workbench goes to the datum mark of NC rotary table, from datum mark, the servomotor encoder rotates the sampling number of a complete cycle according to the NC rotary table of computer installation, send signal by the equal angles spacing, computer is sampled simultaneously to the signal of circle grating 9 and two pen type length gauges 37, till NC rotary table is got back to datum mark; Computer according to adopt data, handle automatically, thereby obtain NC rotary table, the positioning accuracy of corresponding angle, and show measurement result and error curve from datum mark.The servomotor of NC rotary table drives the workbench counter-rotating again, NC rotary table is from datum mark when measuring counter-rotating, the positioning accuracy of corresponding angle, and when showing counter-rotating NC rotary table from datum mark, the measurement result of corresponding angle positioning accuracy and error curve.At last, as required, computer output measurement result.

(2). static measurement: locating pin 32 is put into the endoporus at NC rotary table 33 centers, measuring mechanism is placed on the table top of NC rotary table, measuring mechanism is positioned on the table top of rotary table with the inner hole surface P of positioning sleeve 31 and the periphery Q of locating pin 32; Behind chuck 20 declines and the clamping connecting rod 19, the chuck 20 that rises again breaks away from the steel ball 23 and second connecting plate 17 on the locating pin 24.The driven by servomotor workbench rotation of NC rotary table, when workbench goes to the datum mark of NC rotary table, from datum mark, servomotor rotates the sampling number of a complete cycle according to the NC rotary table of computer installation, stop after rotating an equal angles spacing, manual or computer is sampled simultaneously to the signal of circle grating 9 and two pen type length gauges 37 automatically; Afterwards, servomotor drives and stops after workbench rotates an equal angles spacing again, and manual or computer is sampled simultaneously to the signal of circle grating 9 and two pen type length gauges 37 automatically; Circulation successively is till workbench is got back to datum mark; Computer according to adopt data, handle automatically, thereby obtain NC rotary table, the positioning accuracy of corresponding angle, and show measurement result and error curve from datum mark.The servomotor of NC rotary table drives the workbench counter-rotating again, NC rotary table is from datum mark when measuring counter-rotating, the positioning accuracy of corresponding angle, and when showing counter-rotating NC rotary table from datum mark, the measurement result of corresponding angle positioning accuracy and error curve.At last, as required, computer output measurement result.

Measuring mechanism is installed on the workbench, and the round grating centre of gyration and the NC rotary table centre of gyration of mechanism have eccentric amount e.During measurement, the workbench rotation, two pen type length gauges detect the eccentric x of the round grating centre of gyration and the NC rotary table centre of gyration in good time _i, y _iBecause eccentric, the angle of circle grating is not the angle that NC rotary table turns over, there is certain mathematical relationship in they.Be illustrated in fig. 7 shown below.

Among Fig. 7, O-NC rotary table centre of gyration O '-circle grating spindle swing center

a _iThe designed distance of-encoder main shaft gyration center r-O-O '

e _Xi-directions X eccentric amount e _Yi-Y direction offset

β _i-NC rotary table corner α _i-circle grating corner

Δ _i-circle grating angles of display and NC rotary table actual rotational angle poor

Obviously, justify the eccentric amount e of the grating main shaft gyration center and the NC rotary table centre of gyration _Xi, e _YiWith circle grating corner α _iWith NC rotary table actual rotational angle β _iThe difference Δ _iFollowing relation is arranged:

${\mathrm{\Δ}}_i={\mathrm{tg}}^{-1}\frac{e_{\mathrm{xi}}}{r+e_{\mathrm{yi}}}-------------\left(1\right)$

NC rotary table actual rotational angle β _iFor:

${\mathrm{\β}}_i={\mathrm{\α}}_i+{\mathrm{\Δ}}_i={\mathrm{\α}}_i+{\mathrm{tg}}^{-1}\frac{e_{\mathrm{xi}}}{r+e_{\mathrm{yi}}}-------\left(2\right)$

Computer according to adopt two pen type length gauge x _i, y _iData, fit centre of gyration O and the angular encoder main shaft gyration center a that calculates NC rotary table with the multinomial least square method _iAround the rotating eccentric amount e of O _Xi, e _Yi, calculate the actual rotational angle β of numerical control rotary work then by above-mentioned formula _iAt last, calculate the deviations of corresponding points with following formula:

${\mathrm{\δ}}_i={\mathrm{\β}}_i-\frac{360\×60\×{60}^{\′\′}}{n}\×n_i---------\left(3\right)$

In the formula, δ _iDeviations n-that-Di i the is ordered sampling n that always counts _iThe sampling number that-Di i is ordered

The computer sampling schematic diagram is shown in Fig. 8,9.

Computer according to adopt data α _i, x _i, y _i, at first fit and calculate round grating main shaft gyration center a with the multinomial least square method _iEccentric amount e with the centre of gyration O of NC rotary table _Xi, e _Yi, then by formula (1), NC rotary table is calculated from datum mark in (2), (3), the deviations of each corresponding points.

Computer handle automatically collection data flow chart as shown in figure 10.

The multinomial least square method of fitting is asked eccentric amount e _Xi, e _YiMethod is as follows:

1, method introduction:

A given n data point (i, xi), i=0,1,2 ..., n-1,

Ask a least square of m time to fit multinomial

P _m(i)=a ₀+ a ₁I+a ₂i ²+ ... + a _mi ^m, m≤n wherein, general m is much smaller than n.

At first construct one group of number of times and be no more than the polynomial function system of quadrature on set point of m

{Q _j(i)(j＝0，1，2，…，m)}，

Then available { Q _j(i) (j=0,1,2 ..., m) } do least square as basic function and fit, promptly

P _m(i)＝q ₀Q ₀(i)+q ₁Q ₁(i)+…+q _mQ _m(i)，

Coefficient q wherein _jFor

$q_j=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}{x}_i{Q}_j\left(i\right)}{\underset{j=0}{\overset{n-1}{\mathrm{\Σ}}}{Q}_j^2\left(i\right)},j=\mathrm{0,1,2},\·\·\·,m$

Orthogonal polynomial Q on the structure set point _j(i), (j=0,1 ... m) recurrence formula is as follows:

$\left\{\begin{array}{c}{Q}_0\left(i\right)=1\\ Q_1\left(i\right)=(i-{\mathrm{\α}}_0)\\ Q_{j+1}\left(i\right)=(i-{\mathrm{\α}}_j)Q_j\left(i\right)-{\mathrm{\β}}_j{Q}_{j-1}\left(i\right),j=\mathrm{1,2},\·\·\·,m-1\end{array}\right.$

Wherein ${\mathrm{\α}}_j=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}i{Q}_j^2\left(i\right)}{d_j},j=\mathrm{0,1,2},\·\·\·,m-1$

${\mathrm{\β}}_j=\frac{d_j}{d_{j-1}},j=\mathrm{1,2},...,m-1$

And $d_j=\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}{Q}_j^2\left(i\right),j=\mathrm{0,1,2},\·\·\·,m-1$

2, calculation procedure:

(1) structure Q ₀(i).

If Q ₀(i)=b ₀, obvious b ₀=1.Calculate following amount then respectively:

d ₀＝n

$q_0=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}{x}_i}{d_0}$

${\mathrm{\α}}_0=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}i}{d_0}$

At last with q ₀Q ₀(i) be added in the polynomial fitting after the expansion, promptly have:

q ₀b ₀a ₀

(2) structure Q ₁(i).

If Q ₁(i)=t ₀+ t ₁I, obviously t ₀=-α ₀, t ₁=1.Calculate following amount then respectively:

${\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">d</figure-callout>}}_1=\underset{i=0}{\overset{n-1}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">Q</figure-callout>}}_1^2\left(i\right)$

${\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">q</figure-callout>}}_1=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\&Sigma;}}}{x}_i{Q}_1\left(i\right)}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}$

${\mathrm{\&alpha;}}_1=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\&Sigma;}}}\mathrm{<figure-callout\; id="1"\; label="i\; Q"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">i</figure-callout>}{Q}_{}^{}{}_1^2\left(i\right)}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="A20071004939500131.png,A20071004939500171.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}$

${\mathrm{\&beta;}}_1=\frac{d_1}{d_0}$

At last with q ₁Q ₁(i) be added in the polynomial fitting after the expansion, promptly have:

a ₀+q ₁t ₀α ₀

q ₁t ₁a ₁

(3) for j=2,3 ..., m, progressively recursion Q _j(i).

Have according to recurrence formula

Q _j(i)＝(i-α _j-1)Q _j-1(i)-β _j-1Q _j-2(i)

＝(i-α _j-1)(t _j-1i ^j-1+…+t ₁i+t ₀)-β _j-1(b _j-2i ^j-2+…+b ₁i+b ₀)

Suppose Q _j(i)=s _ji ^j+ s _J-1i ^J-1+ ... + s ₁I+s ₀

Then can obtain calculating s _i(i=0,1 ..., formula j) is as follows:

$\left\{\begin{array}{c}{s}_j=t_{j-1}\\ s_{j-1}=-{\mathrm{\&alpha;}}_{j-1}{t}_{j-1}+t_{j-2}\\ s_i=-{\mathrm{\&alpha;}}_{j-1}{t}_i+t_{i-1}-{\mathrm{\&beta;}}_{j-1}{b}_i,(i=j-2,\&CenterDot;\&CenterDot;\&CenterDot;,\mathrm{2,1})\\ s_0=-{\mathrm{\&alpha;}}_{j-1}{t}_0-{\mathrm{\&beta;}}_{j-1}{b}_0\end{array}\right.$

Calculate following amount then respectively:

$d_j=\underset{i=0}{\overset{n-1}{\mathrm{\&Sigma;}}}{Q}_j^2\left(i\right)$

$q_j=\frac{\underset{i=0}{\overset{n-1}{\mathrm{\&Sigma;}}}{x}_i{Q}_j\left(i\right)}{d_j}$

${\mathrm{\&alpha;}}_j=\frac{\underset{j=0}{\overset{n-1}{\mathrm{\&Sigma;}}}i{Q}_j^2\left(i\right)}{d_j}$

${\mathrm{\&beta;}}_j=\frac{d_j}{d_{j-1}}$

Again with q _jQ _j(i) be added in the polynomial fitting after the expansion, promptly have:

a _i+q _js _ia _i，(i＝j-1，…，1，0)

q _js _j?a _j

Arrive this, obtained multinomial P _m(i)=a ₀+ a ₁I+a ₂i ²+ ... + a _mi ^mIn coefficient a ₀, a ₁, a ₂..., a _m

(4) ask e _Xi

In fact e _Xi=P _m(i), i=0,1,2 ..., n-1.

So, with i=0,1,2 ..., n-1 brings multinomial respectively into

P _m(i)=a ₀+ a ₁I+a ₂i ²+ ... + a _mi ^m, just obtained e _X1, e _X2..., e _Xn-1

(5) ask e _Yi

With the x in above-mentioned (1)-(4) _iUse y _iReplace, repeat

(1)-(4) step just can have been obtained e _Y1, e _Y2..., e _Yn-1

Claims (3)

1, the method of quick measuring positioning accuracy of Numerically controlled revolving dial measuring mechanism, the main shaft of measuring mechanism (10) is connected with base plate (1), positioner is positioned main shaft (10) in the hole at NC rotary table center, main shaft (10) is connected with the groove ring of circle grating, circle grating seat and axle sleeve and first connecting plate (15) are connected, first connecting plate (15) is connected with optical axis (14), second connecting plate (17) is connected with chuck (20), two pen type length gauges (32) are connected with first or second connecting plate, its axis becomes 90 ° of angles by the centre of gyration of main shaft (10), the axis of a pen type length gauge and the axis of optical axis are in same vertical guide, the gauge head of pen type length gauge closely contacts with the internal face M of the gage button that second connecting plate or first connecting plate are connected, optical axis is positioned at second and connects between two needle rollers of (17) or the straight pin (49) and gapped with it, and its measuring process is as follows:

(1) when the driven by servomotor NC rotary table goes to the datum mark of NC rotary table, from datum mark, the sampling number n that the servomotor encoder rotates a circle according to the default NC rotary table of computer, computer dynamic or the static shaft angle α that the circle grating is turned over _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark,

(2) with the x of pen type length gauge _iValue and corresponding i value obtain the directions X eccentric amount e with polynomial least square fitting _XiI=0 wherein, 1,2,3 ... n-1,

(3) with the y of pen type length gauge _iValue and corresponding i value obtain Y direction eccentric amount e with polynomial least square fitting _Yi, i=0 wherein, 1,2,3 ... n-1,

(4) the difference Δ of calculating circle grating corner and NC rotary table actual rotational angle _i,

${\mathrm{\&Delta;}}_i={\mathrm{tg}}^{-1}\frac{e_{\mathrm{xi}}}{r+e_{\mathrm{yi}}},$

R is the designed distance of circle grating oscillation center,

(5) calculate NC rotary table actual rotational angle β _i,

β _i＝α _i+Δ _i，

α _iBe circle grating corner,

(6) the corner deviation δ of calculating NC rotary table _i,

${\mathrm{\&delta;}}_i={\mathrm{\&beta;}}_i-\frac{360\&times;60\&times;60^{\&prime;\&prime;}}{n}\&times;n_i,$

n _iBe the arbitrary positive integer among the 1-n,

(7) ask δ _iMaximum δ _MaxWith minimum of a value δ _Min,

(8) the positioning accuracy δ of calculating NC rotary table,

δ＝δ _max-δ _min。

2, measuring method according to claim 1, it is characterized in that in the step (1), from datum mark, the sampling number n that the servomotor encoder rotates a circle according to the default NC rotary table of computer, send signal by the equal angles spacing, the shaft angle α that computer turns over the circle grating automatically _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark.

3, measuring method according to claim 1, it is characterized in that in the step (1), from datum mark, the sampling number n that the servomotor encoder rotates a circle according to the default NC rotary table of computer, stop after turning over an equidistant angle, computer is by shaft angle α manual or that automatically the circle grating is turned over _iX with two pen type length gauges _i, y _iValue is sampling simultaneously, till NC rotary table is got back to datum mark.

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