CN101261507A - Method for computer numerically controlled straight-line conversion to NURBS machining paths - Google Patents

Abstract

The invention provides a computer numerical control (CNC) method; the method can automatically convert a linear processing route file to an NURBS curve processing route file, which is mainly applied on processing route planning software of a CNC controller, an NURBS curve is generated by converting a linear processing command via the software, then a user can use the NURBS curve command for carrying out the processing on the CNC controller, a processing procedure (NC file) which mainly automatically converts to the NURBS curve router processing command by the invention can provide the high-precision curves, thus facilitating the velocity planning of the CNC controller and achieving the demands of high-speed processing.

Description

Method for computer numerically controlled straight-line conversion to NURBS machining paths

Technical field

The present invention relates to a kind of method for computer numerically controlled straight-line conversion to NURBS machining paths.

Background technology

The CNC controller is to process with the cutter path of straight line or circular arc traditionally, and these processing orders are normally noted down (as: straight line: G01 in the mode of G sign indicating number; Circular arc: G02, G03).But, in recent years because workpiece shape complicated, need to use more advanced curve model emulation, wherein NURBS (Non-uniform rational B-spline) is the most widely used parameter type model, and most CAD/CAM system are all with the main mathematical models of nurbs curve model as curve data structure and data output.

CAD/CAM software is to describe the workpiece path of intending processing with the mathematical model of parameter type, the CNC controller in past can only be accepted the instruction of straight line and circular arc, so when these parameterized workpiece processing shelves when converting the short lines instruction that the CNC controller can accept to, must in CAM software, set its machining precision, original parameter type curve, curved profile are dispersed as many short lines section paths.And wherein a large amount of short lines sections processing order makes the following process board must underspeed at speed planning as far as possible, in order to avoid bigger vibration takes place board in the process, so working (machining) efficiency is generally all relatively poor.

CNC machine table application parameter formula interpolator is more and more universal, still have many industries to rely on original old CAM system at present, therefore when its workpiece processing routing instruction of output, still be similar to the mode of workpiece profile with many short lines sections (G01), not only process time longer because the instruction of a large amount of short lines section makes that dynamic data transmission load is excessive, produce the phenomenon of intermittently pausing in process easily, influence the smooth-going degree of surface of the work.

Because the CNC machine tool in past can only be accepted the machining path instruction of straight line and circular arc, old user relies on the approximate path of straight line and circular arc line segment emulation workpiece profile.Wherein, a large amount of short lines section paths makes and must underspeed when follow-up speed planning, in order to avoid bigger vibration takes place board in the process, so working (machining) efficiency is generally all relatively poor.Yet CNC machine tool now has ability application parameter formula mathematical model, as: nurbs curve (the B-spline curve is a kind of special case wherein), planning speed is processed.The CNC machine tool is because use nurbs curve to carry out path planning, and the suitable nurbs curve interpolator of arranging in pairs or groups on motion control, speed planning, is good than originally using straight line and circular arc line segment planning machining path all.

Summary of the invention

Fundamental purpose of the present invention is to overcome the above-mentioned shortcoming that existing product exists, and provide a kind of method for computer numerically controlled straight-line conversion to NURBS machining paths, allow existing user still not break away under the operator scheme of CAM in the use, utilize the method for numerically controlled straight-line conversion to NURBS machining paths to make the user still can under the constant pattern that changes jobs, obtain up-to-date nurbs curve; Utilize the computer powerful operation capacity, and through automated procedures, the order format (G01) that promotes old CAM output straight line line segment is the order format (G06.2) of nurbs curve section, with meet CNC machine tool now at a high speed, the demand of pinpoint accuracy.

The objective of the invention is to realize by following technical scheme.

The straight line conversion nurbs curve machining path method of computer Numerical Control of the present invention is characterized in that, comprising:

(1) reads archives: read original processing archives, producing a processing work profile order, and this order stored;

(2) filtration path point data: rational filtration path point data, and highlight the separating property of machining path cathetus paragraph and curve paragraph;

(3) according to the waypoint of geometrical property commit point data: the point data after the filtration, the some group character of its straight line and curve paragraph is more obvious, changes by point data continuous point group is divided into two kinds of different groups;

(4) decision waypoint continuity: the segment of curve that separates out needs given its chimeric condition of continuity before chimeric, and the position condition of continuity can be obtained by point data itself, and the above continuously condition of slope then need be tried to achieve in advance by the point data of waypoint position;

(5) curve is chimeric according to error: according to the given condition of continuity, add the control of the margin of error and the flatness of setting, produce fast the curve that satisfies all conditions, all automatic chimeric one-tenth curve of aforementioned each section point data reaches the condition of continuity of position or slope between curve and curve;

(6) nurbs curve is transcoded into the order format of parameter type curve sign indicating number: separate out straight line and Curve Machining path, add each parameter of curve model of having tried to achieve, the unelected mode of selecting with G01 or G06.2 of straight-line segment stores (mode with G01 stores, the archives that the acquisition capacity is less); Curve then stores in the mode of G06.2.

The straight line conversion nurbs curve machining path method of aforesaid computer Numerical Control is characterized in that, in the filtered points data of described step 2, defines one in advance and allows the chord length error amount, as the filtration path point data.

The straight line conversion nurbs curve machining path method of aforesaid computer Numerical Control, it is characterized in that, in the filtered points data of described step 2, with one make by oneself allow the chord length error amount, judge that whether distance between any point and adjacent 2 chord lengths is greater than allowing that the chord length error amount decides each point data going or staying.

The straight line conversion nurbs curve machining path method of aforesaid computer Numerical Control, it is characterized in that, in the described step 3, the variation of point data is judged according to the angle of point data and length, and respectively the point data differentiation is become two kinds of different groups of straight-line segment and segment of curve.

The straight line of aforesaid computer Numerical Control conversion nurbs curve machining path method is characterized in that, the mode that described straight-line segment can G01 stores, and segment of curve then produces its parameter of curve model in chimeric mode.

The straight line conversion nurbs curve machining path method of computer Numerical Control of the present invention is characterized in that, comprising:

(1) reads archives: read original processing archives, producing a processing work profile order, and this order stored;

(2) filtration path point data: rational filtration path point data, and highlight the separating property of machining path cathetus paragraph and curve paragraph;

(3) according to the waypoint of geometrical property commit point data: the point data after the filtration, the some group character of its straight line and curve paragraph is more obvious, by the judgement rule of point data angle and length variations, continuous point group is divided into straight-line segment and segment of curve;

(4) decision waypoint continuity: the segment of curve that separates out needs given its chimeric condition of continuity before chimeric, and the position condition of continuity can be obtained by point data itself, and the above continuously condition of slope then need be tried to achieve in advance by the point data of waypoint position;

(5) curve is chimeric according to error: according to the given condition of continuity, add the control of the margin of error and the flatness of setting, produce fast the curve that satisfies all conditions, all automatic chimeric one-tenth curve of aforementioned each section point data reaches the condition of continuity of position or slope between curve and curve;

(6) nurbs curve is transcoded into the order format of parameter type curve sign indicating number: separate out straight line and Curve Machining path, add each parameter of curve model of having tried to achieve, the optional mode of selecting with G01 or 606.2 of straight line paragraph stores (mode with G01 stores, and can obtain the less archives of capacity); Curve then stores in 606.2 mode.

The straight line of aforesaid computer Numerical Control conversion nurbs curve machining path method is characterized in that, in the filtered points data of described step 2, defines one in advance and allows the chord length error amount, with as the filtration path point data.

The straight line conversion nurbs curve machining path method of aforesaid computer Numerical Control, it is characterized in that, in the filtered points data of described step 2, with one make by oneself allow the chord length error amount, judge that whether distance between any point and adjacent 2 chord lengths is greater than allowing that the chord length error amount decides each point data going or staying.

The straight line conversion nurbs curve machining path method of aforesaid computer Numerical Control is characterized in that the mode that described straight-line segment can be kept with G01 stores; Segment of curve then produces its parameter of curve model in chimeric mode.

The beneficial effect of method for computer numerically controlled straight-line conversion to NURBS machining paths of the present invention, technological means used in the present invention is to utilize the computer powerful operation capacity, and through automated procedures, the order format (G01) that promotes old CAM output straight line line segment be the order format (G06.2) of nurbs curve section, with meet CNC machine tool now at a high speed, the demand of pinpoint accuracy.

Description of drawings:

Fig. 1 is main operation workflow figure of the present invention.

Fig. 2 is converted to the decision flow chart of point data form for G01 order format.

Fig. 3 is the initial chord length error of a data synoptic diagram.

Fig. 4 upgrades chord length error synoptic diagram for point data.

Fig. 5 is a point data turning angle synoptic diagram.

Fig. 6 is a point data focal length synoptic diagram.

Fig. 7 is that curve is according to the chimeric process flow diagram of error.

Fig. 8 is line segment error analysis result.

Fig. 9 is a processing work profile synoptic diagram.

Figure 10 is the single passage data from the acquisition of processing work profile.

Figure 11 is a data segmentation result.

Figure 12 is the given result of continuity.

Embodiment

1, reads job sequence and be converted to the coordinate points data layout.

In job sequence (NC file) lining from industry, the instruction that direct relation is arranged with the geometric shape (as shown in Figure 9) and the machining path of workpiece is the G sign indicating number, and wherein G01 is used to refer to the stationary knife tool and moves with the pattern of linear interpolation, and the form of program is as follows:

G01 X_Y_Z_(F_S_…)

X_Y_Z_

X_Y_Z_

X_Y_Z_

…

G01 2-10.059 F600

X17.543 Y-17.55 F2000

X17.541 Y-17.548 Z-10.056

X17.508 Y-17.515 Z-9.99

X17.449 Y-17.456 Z-9.871

X16.654 Y-16.66 Z-8.266

X16.624 Y-16.631 Z-8.208

The present invention uses from the coordinate points data layout ordered and changes the routing instruction that belongs to the G01 interpolation in the NC archives, read in the document converting process determination methods as shown in Figure 2.When reading the NC archive content by row, the kenel of main judgement earlier path point coordinate system is incremental coordinates system or absolute coordinate system, and it influences the account form of path point coordinate value.Then judge whether the path point that occurs pattern, if judge the path point that belongs to G01, then capture X, Y, numerical value that Z is relevant deposits in from the point coordinate data form of ordering for G01.

2, according to allowing chord length error filtration noise point data.

Because the short lines section that CAD/CAM produced, normal and original path has than mistake the point data that previous step obtains suddenly, the action that must filter noise point earlier.Figure 3 shows that example, the P in the some data _iThe point to adjacent point-to-point transmission online apart from e _i, be initial chord length error.At first must reject in the some data, the initial chord length error of each point greater than according to working environment predefined point of allowing chord length error ε, then will be less than the continuous point group of allowing the chord length error, as shown in Figure 4, with institute's marker location among the figure, which point judges has to be omitted in each continuous point group.Figure 4 shows that example, P ₁～P ₅Be the continuous point group that satisfies above-mentioned condition, if f ₁With f ₂Any numerical value is arranged greater than ε, then represent P ₀～P ₃Has only P ₁Can be omitted, again with P ₂Be starting point, carry out P with above-mentioned mode ₂～P ₅Between judgement; If both all less than allowing the chord length error, then further judge g ₁～g ₃With the magnitude relationship of allowing the chord length error amount.Just can guarantee in this manner to allow under the condition of chord length error amount satisfied, the noise in the reasonable filtered points data, and further highlight geometrical property smooth or crooked in the whole point data.

3, according to the waypoint of geometrical property commit point data.

Continuous point data is distinguished into straight line path line segment and curved path line segment, with the original machining path of reduction workpiece.The straight line path line segment then can directly be converted to G01 instruction type as output.The point data of curved path line segment then needs to produce the curve that satisfies error limitation further in the chimeric mode of curve.At first, outside the head of curve, 2 on tail, calculate each point and the turning angle θ of any down _i, as shown in Figure 5,

${\mathrm{\θ}}_i={\cos }^{-1}\left(\frac{(P_{i+1}-P_i)\·(P_i-P_{i-1})}{|P_{i+1}-P_i|\×|P_i-P_{i-1}|}\right).$

If θ _iGreater than a door angle θ who is predetermined _Tol, P then _iBe considered as waypoint; Otherwise whether be long straight-line segment, as shown in Figure 6, suppose l if then need observe the adjacent lines segment length again _iBe line segment length, Ave _jBeing adjacent lines segment length's mean value, is example with N=5, judges that rule is as follows:

(1)Ave ₁＝(l ₁+l ₂+l ₃+l ₄+l ₅)/N

Ave ₂＝(l ₇+l ₈+l ₉+l ₁₀+l ₁₁)/N

Ave ₃＝(l ₂+l ₃+l ₄+l ₅+l ₆)/N

Ave ₄＝(l ₈+l ₉+l ₁₀+l ₁₁+l ₁₂)/N

(2) if (l ₆＞r _Tol* Ave ₁) or (l ₆＞r _Tol* Ave ₂) or (l ₇＞r _Tol* Ave ₃) or (l ₇＞r _Tol* Ave ₄), P then _iPoint promptly is considered as waypoint for long line segment end points.Wherein, r _TolIt is a ratio threshold value.

4, decision waypoint continuity.

When the angle turnover of the end points of adjacent paragraph, as shown in Figure 6, greater than θ _TolThe time, then the continuity of given this waypoint is that the position is continuous; Otherwise it is continuous then to be given as slope.Since during follow-up chimeric curve, except considering error, in order to ensure the connection and the flatness of position between each processing instruction, must be given in advance in the end points condition of continuity of curve paragraph.Wherein the position condition of continuity can be obtained by the end points of segment of curve drop point data, and the slope condition of continuity then must decide by getting the chimeric in advance curve of local data near the waypoint.But if the curve paragraph is adjacent with the straight line paragraph and be the slope condition for continuous, then the slope condition of continuity then can need not chimeric in advance curve by the acquisition of connection rectilinear point data.

5, the curved boundary that satisfies specification error is restrained sex-mosaicism continuously.

The mathematic(al) mode of nurbs curve is expressed as follows:

$C\left(u\right)=\frac{\underset{i=0}{\overset{n}{\mathrm{\Σ}}}{N}_{i,k}\left(u\right)w_i{A}_i}{\underset{i=0}{\overset{n}{\mathrm{\Σ}}}{N}_{i,k}\left(u\right)w_i}---\left(1\right)$

$=\underset{i=0}{\overset{n}{\mathrm{\Σ}}}{R}_{i,k}\left(u\right)A_i=\left[R\right]\left[A\right]$

A wherein _iBe curve control point, w _iBe weight parameter, N _{I, k}(u) be basis function, u is a parameter of curve, R _{I, k}(u) be reasonable basis function, n+1 is the reference mark number, and k is the curve exponent number, and [R], [A] are respectively R _{I, k}(u), A _iMatrix form.

Point data is considered chimericly under curve precision, flatness and the boundary condition to go out nurbs curve at the same time.Curve is chimeric to be in conjunction with squared error function (2) and energy function (3), under the situation that minimizes square error and energy function, obtains the nurbs curve of optimization.

$\mathrm{\ϵ}=\underset{j=0}{\overset{m}{\mathrm{\Σ}}}{[C\left(u_j\right)-Q_j][C\left(u_j\right)-Q_j]}^T---\left(2\right)$

$E=\underset{j=0}{\overset{k}{\mathrm{\Σ}}}\left(\mathrm{\α}\right[C^{\′}\left(u_j\right)\left]\right[C^{\′}\left(u_j\right){]}^T+\mathrm{\β}\left[C^{\′\′}\left(u_j\right)\right]{\left[C^{\′\′}\left(u_j\right)\right]}^T)\mathrm{\Δu}---\left(3\right)$

$\min (\mathrm{\ϵ}+E)\⇒\frac{\∂\mathrm{\ϵ}}{{\∂A}_1}+\frac{\∂E}{{\∂A}_1}=\mathrm{0,1}=\mathrm{0,1},...,n$

$\⇒\left\{{\left[R\right]}^T\right[R]+\mathrm{\α}{\left[R^{\′}\right]}^T[R^{\′}]+\mathrm{\β}{\left[R^{\′\′}\right]}^T[R^{\′\′}\left]\right\}\left[A\right]={\left[R\right]}^T\left[Q\right]---\left(4\right)$

$\⇒\left[R_N\right]\left[A\right]=\left[Q_N\right]$

∴[A]＝[R _N] ^-1[Q _N]

Wherein ε is an error function, and E is the curve energy function, and α and β are the chimeric smoothing coefficient of curve, Q _jBe a data, [Q] is Q _jMatrix form, [R], [RN ' _α] with [RN " _β] then be respectively the reasonable basis function matrix of curve and once with twice differential matrix.

The point group data Q that judges according to previous step _i, i=0,1 ..., when m, chimeric one-tenth nurbs curve, need satisfy the root-mean-square error value e of point data to chimeric curve _RmsMinimize,

$e_{\mathrm{rms}}=\sqrt{\frac{1}{m+1}\underset{j=0}{\overset{m}{\mathrm{\Σ}}}{e}_j{e_j}^T},$

e _j＝||Q _j-C(u _j)||，

E wherein _jBe a data Q _jDistance to chimeric curve corresponding point.

Therefore this step adopts suitable knot vector, and counts out with iterative manner renewal knot vector and curve controlled, and reaches the precision that satisfies chimeric curve.Produce in the calculating process of nurbs curve at point group data simultaneously, as the chimeric contained condition of curve, make chimeric nurbs curve satisfy the boundary condition that sets the curved boundary condition.

Satisfies curved boundary that error sets and restrain the algorithm steps of sex-mosaicism continuously and be described as follows, and the chimeric process flow diagram of curve is as shown in Figure 7:

Step 1: the chimeric parameter of curve of set point data

1, according to the number percent of point group data at total length, set point data parameter of curve u.

u ₁＝0

$u_i=\frac{\underset{g=2}{\overset{i}{\mathrm{\Σ}}}|P_g-P_{g-1}|}{\underset{g=2}{\overset{m}{\mathrm{\Σ}}}|P_g-P_{g-1}|},i=2,...,m---\left(5\right)$

2, set the boundary condition of chimeric curve by near the point data the frontier point.

3, minimize condition by energy function, set the flatness factor alpha and the β of chimeric curve.

4, set chimeric curve exponent number and set chimeric error.

5, by the contrary flexure state of point group data, set the start node vector.

Step 2: point group data can obtain one group system of equations, utilizes numerical analysis method to solve curve control point, and obtains chimeric curve.

Step 3: calculate the distance of point group data, be considered as the chimeric error of curve to chimeric curve.

Step 4: exceeding nodal value of insertion between two knot vectors of error, and counting out with iterative manner renewal knot vector and curve controlled.

Step 5: if the chimeric error of curve greater than the error that sets, then repeating step two is to step 4, the XM vector upgrades with the iteration that curve controlled is counted out.If the chimeric error of curve less than the error that sets, is then finished the chimeric step of curve, obtain the optimization nurbs curve.

Above-mentioned by 1. read job sequence be converted to the coordinate points data layout, 2. according to allow the chord length error filter the noise point data, 3. according to the waypoint of geometrical property commit point data, 4. decision waypoint continuity, the curved boundary that 5. satisfies specification error are restrained the formed practical situation of step such as sex-mosaicism continuously and are then drawn by Figure 10, Figure 11, situation shown in Figure 12 discriminably.

6.NURBS curve is transcoded into the order format of parameter type curve sign indicating number:

After the geological information of straight line and curve produced again, then needing these information translation was the order format of NC archives.The straight line paragraph is kept original G01 instruction type as output, and is as follows;

G01 X_Y_Z_(F_S_…)

X_Y_Z_

X_Y_Z_

X_Y_Z_

…

G01 2-10.059 F600

X17.543 Y-17.55 F2000

X17.541 Y-17.548 Z-10.056

X 17.508 Y-17.515 Z-9.99

X17.449 Y-17.456 Z-9.871

X16.654 Y-16.66 Z-8.266

X16.624 Y-16.631 Z-8.208

Nurbs curve then converts the order format G06.2 that present most of nurbs curve interpolator can receive to:

G06.2 P_K_X_Y_Z_(R_F_)

K_X_Y_Z(R_)

…

K_X_Y_Z(R_)

K_

…

K_

G6.2 P04 K0.0 X-41.405 Y19.524 Z-6.978

K0.0 X-41.339 Y19.655 Z-6.984

K0.0 X-40.569 Y21.08 Z-6.945

K0.0 X-39.877 Y22.457 Z-6.982

K.095 X-39.14 Y23.731 Z-6.975

K1.

K1.

K1.

K1.

Consult line segment error analysis result shown in Figure 8, wherein, Max is maximum single-point error amount, and RMS is the root-mean-square error value, and error amount presents with the right color difference table, can be distributed by the error amount of finding out each point among the figure, and error is below 0.0018mm.

Before the conversion	After the conversion
		414,309	24,690

Table 1 changes the processing number of instructions that archives comprised before and after the back

Have only G01 (so the short lines section is a lot) before the conversion, G01 and G06.2 mix (becoming nurbs curve because merge many short lines sections, so instruction tails off a lot) after the conversion.

The above, it only is preferred embodiment of the present invention, be not that the present invention is done any pro forma restriction, every foundation technical spirit of the present invention all still belongs in the scope of technical solution of the present invention any simple modification, equivalent variations and modification that above embodiment did.

Claims (9)

1. the straight line of computer Numerical Control conversion nurbs curve machining path method is characterized in that, comprising:

(1) read archives:

Read original processing archives, producing a processing work profile order, and this order stored;

(2) filtration path point data:

Rational filtration path point data, and highlight the separating property of machining path cathetus paragraph and curve paragraph;

(3) according to the waypoint of geometrical property commit point data:

Point data after the filtration, the some group character of its straight line and curve paragraph is more obvious, changes by point data continuous point group is divided into two kinds of different groups;

(4) decision waypoint continuity:

The segment of curve that separates out needs given its chimeric condition of continuity before chimeric, and the position condition of continuity can be obtained by point data itself, and the above continuously condition of slope then need be tried to achieve in advance by the point data of waypoint position;

(5) curve is chimeric according to error: according to the given condition of continuity, add the control of the margin of error and the flatness of setting, produce fast the curve that satisfies all conditions, all automatic chimeric one-tenth curve of aforementioned each section point data reaches the condition of continuity of position or slope between curve and curve;

(6) nurbs curve is transcoded into the order format of parameter type curve sign indicating number:

Separate out straight line and Curve Machining path, add each parameter of curve model of having tried to achieve, the unelected mode of selecting with G01 or G06.2 of straight-line segment stores (mode with G01 stores, the archives that the acquisition capacity is less); Curve then stores in the mode of G06.2.

2. the straight line conversion nurbs curve machining path method of computer Numerical Control according to claim 1 is characterized in that, in the filtered points data of described step 2, defines one in advance and allows the chord length error amount, as the filtration path point data.

3. the straight line conversion nurbs curve machining path method of computer Numerical Control according to claim 1, it is characterized in that, in the filtered points data of described step 2, with one make by oneself allow the chord length error amount, judge that whether distance between any point and adjacent 2 chord lengths is greater than allowing that the chord length error amount decides each point data going or staying.

4. change nurbs curve machining path method according to the straight line of claim 1 or 3 described computer Numerical Control, it is characterized in that, in the described step 3, the variation of point data is judged according to the angle of point data and length, and respectively the point data differentiation is become two kinds of different groups of straight-line segment and segment of curve.

5. the straight line of computer Numerical Control according to claim 4 conversion nurbs curve machining path method is characterized in that, the mode that described straight-line segment can G01 stores, and segment of curve then produces its parameter of curve model in chimeric mode.

6. the straight line of computer Numerical Control conversion nurbs curve machining path method is characterized in that, comprising:

(1) read archives:

Read original processing archives, producing a processing work profile order, and this order stored;

(2) filtration path point data:

Rational filtration path point data, and highlight the separating property of machining path cathetus paragraph and curve paragraph;

(3) according to the waypoint of geometrical property commit point data:

Point data after the filtration, the some group character of its straight line and curve paragraph is more obvious, by the judgement rule of point data angle and length variations, continuous point group is divided into straight-line segment and segment of curve;

(4) decision waypoint continuity:

The segment of curve that separates out needs given its chimeric condition of continuity before chimeric, and the position condition of continuity can be obtained by point data itself, and the above continuously condition of slope then need be tried to achieve in advance by the point data of waypoint position;

(5) curve is chimeric according to error: according to the given condition of continuity, add the control of the margin of error and the flatness of setting, produce fast the curve that satisfies all conditions, all automatic chimeric one-tenth curve of aforementioned each section point data reaches the condition of continuity of position or slope between curve and curve;

(6) nurbs curve is transcoded into the order format of parameter type curve sign indicating number:

Separate out straight line and Curve Machining path, add each parameter of curve model of having tried to achieve, the optional mode of selecting with G01 or G06.2 of straight line paragraph stores (mode with G01 stores, and can obtain the less archives of capacity); Curve then stores in the mode of G06.2.

7. the straight line of computer Numerical Control according to claim 6 conversion nurbs curve machining path method is characterized in that, in the filtered points data of described step 2, defines one in advance and allows the chord length error amount, with as the filtration path point data.

8. the straight line conversion nurbs curve machining path method of computer Numerical Control according to claim 6, it is characterized in that, in the filtered points data of described step 2, with one make by oneself allow the chord length error amount, judge that whether distance between any point and adjacent 2 chord lengths is greater than allowing that the chord length error amount decides each point data going or staying.

9. the straight line conversion nurbs curve machining path method of computer Numerical Control according to claim 8 is characterized in that the mode that described straight-line segment can be kept with G01 stores; Segment of curve then produces its parameter of curve model in chimeric mode.

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