JP2595568B2 - Offset data creation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an offset data creating method, for example, CA
D (computer aided design) or CAM (computer aide
d manufacturing) and the like, and is preferably applied to a case where offset data for manufacturing a product having an outer shape having the free-form surface is created using data representing the free-form surface.

B. Summary of the Invention In the present invention, in an offset data creating method, offset is created by dividing a patch based on a distance between a middle point of a straight line connecting sampling points and a middle point of a straight line connecting representative points. As a result, a product having a smooth outer shape can be manufactured as a whole.

C Conventional Art Conventionally, in a milling machine or the like formed of an NC machine tool, a product having an outer shape having the free-form surface can be manufactured using data representing the free-form surface.

In other words, when designing the shape of an object using CAD techniques (geometric modeling), designers generally use
By specifying a plurality of points (hereinafter referred to as nodes) in a three-dimensional space through which a curved surface passes, and calculating a boundary curve network connecting the specified nodes by a computer using a desired vector function, Create a curved surface represented by a so-called wire frame.

The boundary curve network formed in this way represents a rough shape to be designed by the designer itself.By interpolating a curved surface that can be expressed by a predetermined vector function using the boundary curve, As a whole, a free-form surface (which cannot be defined by a quadratic function) designed by a designer can be generated.

That is, as shown in FIG.
Shared boundaries determined by the two nodes P ₀₀ , P ₃₀ , P ₃₃ and P ₀₃
For COM1, COM2, COM3, and COM4, the parameters in the u and v directions are u and v, and the nodes P ₀₀ , P ₃₀ ,
Each value of the parameter u and v of P ₃₃ and P ₀₃ (0,
0), (1,0), at the (1,1) and (0,1), the following equation _{S (u, v) = (} 1-u + uE) 3 (1-v + vF) 3 P 00 ...... (1 ), The shared boundaries COM1, COM2, COM3, and COM are calculated using a vector function S _{(u, v)} represented by a cubic Bezier equation.
4 can form a curved surface (hereinafter referred to as a patch).

Here, E and F are shift operators, and can be expressed as EP _{i, j} = P _{i + 1, j} FP _{i, j} = P _{i, j + 1,} and u and v are expressed by the following equation: 0 ≦ u ≦ 1 (2) 0 ≦ v ≦ 1 (3)

Accordingly, if a continuous patch S _{(u, v)} is generated for a boundary curve network connecting a plurality of input points, a free-form surface having a desired outer shape surrounded by the patch S _{(u, v) can} be obtained. Can be obtained.

On the other hand, the patch S generated in this manner is
_When a product having an outer shape represented by _{(u, v)} is to be manufactured using a milling machine, first, as shown in FIG.
The patch S _{(u, v)} is divided into, for example, five in the direction and the v direction, and the sampling points A ₀₀ , A ₀₁ , A ₀₂ , A ₀₃ , A ₀₄ , A ₁₀ ,.
_{A 20, ......, A 30,} ......, A 40, ......, after obtaining the A _44, sample the normal vector R · n distance becomes with R a length of from the center position of the milling tool to the cutting edge Standing at points A _{00 to} A ₄₄ , a representative point represented by the tip position of the normal vector
B ₀₀ , B ₀₁ , B ₀₂ , B ₀₃ , B ₀₄ , B ₁₀ ,…, B ₂₀ ,…,
B _30, obtained ......, B _40, ......, the position data of B _44.

If the representative points B _{00 to} B ₄₄ thus obtained are connected by a straight line between adjacent representative points, the patch S
_A linear network (hereinafter, referred to as an offset polyhedron) having a large outer shape by a distance R in the normal direction to the free-form surface surrounded by _{(u, v)} and approximating the surface shape of the free-form surface with a straight line. Obtainable.

Therefore, if the locus of the center position of the tool moves on the offset polyhedron, the cutting edge of the tool can be moved approximately along the curved patch S _{(u, v)} , _and the offset can be obtained. By driving and controlling the NC milling machine based on data representing a polyhedron (hereinafter referred to as offset data ₎ , it is possible to obtain a product having an outer shape having a free-form surface represented by a patch S _{(u, v)} .

D Problems to be Solved by the Invention However, in the outer shape of the product obtained in this way, the free-form surface surrounded by the patch S _{(u, v)} is cut by linear approximation using an offset polyhedron. Therefore, there is a problem that it is inevitable that an excessively cut portion occurs.

For this reason, when the conventional offset data is created, the amount of excessive cutting is detected and the number of divisions of the patch S _{(u, v)} is determined so that the excessive amount of cutting is equal to or less than a predetermined value.
Offset data was created in a practically sufficient range and at the highest possible speed.

That is, as shown in FIG. 9, for the patch S _{(u, v)} , the offset polyhedron S _{(u, v)} represented by the representative points B _i and B _{i + 1} corresponding to the sampling points A _i and A _{i + 1 . v)} in the case of generating the _OFF, the distance in a substantially intermediate position of the sampling points a _i and a _{i + 1,} from the straight line L _i connecting the sampling points a _i and a _{i + 1} Patsuchi to S _{(u, v)} ε is used to represent an excessive amount of shaving, and when the distance ε is equal to or greater than a predetermined value, the number of divisions of the patch S _{(u, v)} is reduced so that the distance between the sampling points A _i and A _{i + 1} is reduced. Has been made to reset.

However, as shown in FIG. 10, when the overcut amount is detected in this way and the number of divisions is set, in the portion ARA1 having a small curvature, the outer shape approximating a smooth free-form surface as a whole is obtained. While the shape can be cut, there is a problem that a product having an outer shape with a squared surface can be obtained in a portion ARA2 having a large curvature.

In other words, when a cutting process is performed on a curved surface having a large curvature and a curved surface having a small curvature so that the overcut amount becomes the same value, the portion is coarsely cut by an amount corresponding to the large curvature.

As a method for solving this problem, a method of detecting the amount of excessive shaving, detecting the curvature of the portion, and setting the number of patch divisions based on the detected curvature is conceivable.

However, in such a case, in order to determine the number of divisions, it is necessary to repeat the complicated work of calculating the curvature for each minute area surrounded by the sampling points, and the time required for the work of creating the offset data is increased. There was a long problem.

The present invention has been made in view of the above points, and it is an object of the present invention to propose a method of creating offset data capable of obtaining a product having a smooth outer shape as a whole.

E. Means for Solving the Problem In order to solve such a problem, in the present invention, the patch S _{(u, v)} forming the free-form surface is divided into patches S _{(u, v).}
A plurality of sampling points A _i and A _{i + 1} are obtained on _{(u, v)} , and a length R corresponding to a tool to be cut with a free-form surface as a cut target.
Are set at sampling points A _i , A _{i + 1} , and the tool movement path is determined based on the position data of the representative points B _i , B _{i + 1} represented by the normal vector R · n. In an offset data creating method for creating offset data to represent, a middle point F _{i of a} straight line connecting adjacent sampling points A _i , A _{i + 1} ,
Sampling points A _i, based on the distance D _i between the A _{i +} representative points B _i corresponding to _1, the middle point E _i of a straight line connecting B _{i + 1,} Patsuchi S
_The number of divisions of _{(u, v)} is determined.

F act sampling point A _i, A _{i 1,} the midpoint F _i of the straight line connecting the _+, representative points B _i, Patsuchi S _(u based on the distance D _i between the straight line of midpoints E _i connecting the B _{i + 1 , v)} , the patch S _{(u, v)}
Of the patch S _{(u, v)} by detecting a value that changes according to the curvature of
Can be divided.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1, in which parts corresponding to those in FIG. 9 are assigned the same reference numerals, shows the principle of detection of the overcut amount.

In this case, as shown in Figure 2, off the excisional processor for creating data, straight line connecting the shift connexion sampling points A _i and A _{i + 1} in step SP2 from step SP1 L
A middle point F _i of the sampling points A _i and A _{i + 1} is obtained on _B.

Then, proceeding to step SP3, the sampling points A _i and A
After obtaining the representative points B _i and B _{i + 1} of the midpoint E _i on the straight line L _B1 connecting the representative points B _i and B _{i + 1} corresponding to _{i + 1,} in step SP4 moves connexion midpoint E _i and calculates the distance D _i between F _i.

Such distance D _i is Patsuchi S _{(u, v)} in a straight line connecting the angle (i.e. the sampling points A _i and the representative point B _i between normal vectors The greater the curvature, the sampling points A
_{i + 1} and the straight line and make connecting representative points B _{i + 1} angle) theta large Do connexion, by linear L _B1 is closer to the straight line L _B, the value decreases.

Accordance connexion, as shown in FIGS. 3 and 4, the distance D _i as is equal Patsuchi S _{(u, v)} if dividing the curvature of the surface of the Patsuchi S _{(u, v)} is large If this is the case, the distance between the sampling points A _i and A _{i + 1} can be set smaller by that amount, and a smooth surface shape can be obtained as in the case of the small curvature portion.

Thus, to calculate the amount gouges based on the distance D _i whose value varies in accordance with the curvature of the sampling points A _i and A _{i + 1} between the Patsuchi S _{(u, v),} this such that is equal to or less than a predetermined value If the number of divisions is set to, a portion having a large curvature can be cut into the same smooth outer shape as a portion having a small curvature.

That is, the arithmetic processing unit, after obtaining the amount gouges by subtracting the distance D _i from the distance R from the center position of the composed for example, a ball end mill with shifting connexion milling tool to the step SP5 to the cutting edge, followed by step The process proceeds to SP6, and the processing procedure ends.

Specifically, as shown in FIGS. 5 and 6, in the patch S _{(u, v)} having a three-dimensional spread, the arithmetic processing unit shifts from step SP11 to step SP12, and sets adjacent sampling points. A _{i, j} , A _{i + 1, j} , A _{i + 1, j + 1}
And A _{i, j + 1} sampling point A _i constituting the diagonals for small area surrounded _{by, j} and A _{i + 1, j + 1} connecting straight line about the midpoint F _{(i, j)} after obtaining the _1, followed by step SP13 Then, a middle point F _{(i, j) 2} is obtained for a straight line connecting the remaining sampling points A _{i + 1, j} and A _{i, j + 1} .

Subsequently, the arithmetic processing circuit proceeds to step SP14, where the representative point B corresponding to each sampling point A _{i, j} and A _{i + 1, j + 1} is obtained.
midpoint E on a line connecting _{i, j} and B _{i + 1, j + 1
After (i, j) 1} is obtained, the process proceeds to step SP15 to represent the representative points B corresponding to the sampling points A _{i + 1, j} and A _{i, j + 1.}
For a straight line connecting _{i + 1, j} and B _{i, j + 1} , a midpoint E
_{(I, j) 2} is obtained.

Subsequently, the arithmetic processing unit proceeds to step SP16 and proceeds to the midpoint E.
_{(I, j) 1} and F _{(i, j)} the distance D _{(i, j)} of between ₁ after obtaining the _1, followed by the step SP17 moves connexion midpoint E _{(i, j) 2} and F _{(i, j)} Obtain the distance D _{(i, j) 2} between the _two .

Subsequently, the arithmetic processing unit proceeds to step SP18 to subtract the distances D _{(i, j) 1} and D _{(i, j) 2} from the distance R from the center position of the ball end mill to the cutting edge, respectively. Get the value.

Subsequently, the maximum value is set to the sampling points A _{i, j} , A
_The amount is obtained as an excessively small amount of the minute area on the patch S _{(u, v)} surrounded by _{i + 1, j} , Ai _{+ 1, j + 1} and Ai _{, j + 1} , and the process proceeds to step SP19 to end the processing procedure.

In practice, the ball end mill MB is used for cutting each representative point B _{i, j} , B _{i + 1, j} , B _{i + 1, j + 1} when cutting with an NC milling machine.
Not only when moving along a straight line connecting B _{i, j + 1} , but also as needed, the scanning trajectory of the center position of the tool is represented by the representative points B _{i, j} , B _{i + 1, j} , B _{i + 1, j + 1} and B _{i. , j + 1} to move across a straight line.

In such a case, each representative point B _{i, j} ,
The distances D _{(i, j) 1} and D _{(i, j) 2} are calculated for the diagonals of B _{i + 1, j} , B _{i + 1, j + 1} and B _{i, j + 1} , respectively, and the largest value among them is obtained as the overcut amount. By doing so, it is possible to prevent the actual overcutting from exceeding the overcutting amount and to calculate the overcutting amount with high accuracy.

The arithmetic processing unit then proceeds to the sampling points A _{i, j} , A
Similarly, for the micro area on the patch S _{(u, v)} adjacent to the micro area surrounded by _{i + 1, j} , A _{i + 1, j + 1} and A _{i, j + 1} , the over-cutting amount is sequentially calculated in the same manner to correspond to the number of sampling points. Then, the data of the maximum value is obtained as the data of the excessive cutting amount of the patch S _{(u, v)} from the data of the excessive cutting amount obtained as a result. Furthermore the Patsuchi S _{(u, v)} for each free-form surface is configured, the Patsuchi S _{(u, v)} sampling the Patsuchi except give cutting only the amount of data of the Patsuchi, in its or maximum value is greater than a predetermined value Determine whether or not.

When the maximum value is equal to or more than the predetermined value, the number of divisions is reset to obtain the data of the excessive shaving amount, and it is determined whether or not the excess amount is equal to or more than the predetermined value. The patch is divided by the division number to generate offset data representing an offset polyhedron.

Thus, by cutting the product having the outer shape of the free-form surface based on the offset data, it is possible to obtain a product which is cut in a smooth outer shape in a region having a large curvature as in a region having a small curvature. .

According to the above configuration, the sampling points A _{i, j} , A
For a small area surrounded by _{i + 1, j} , A _{i + 1, j + 1} and A _{i, j + 1} , sampling points A _{i, j} and A _{i + 1, j + 1} , and sampling points A _{i + 1, j} and A
Midpoints F _{(i, j) 1} and F _{(i, j) 2 of a} straight line connecting _{i, j + 1}
From the representative points B _{i, j} and B _{i + 1, j + 1} and B _{i + 1, j} and B
Midpoints E _{(i, j) 1} and E of a diagonal line connecting _{i, j + 1
(I, j)} the distance D _{(i, j)} of up to _{2 1} and D _{(i, j)} by creating an off-excisional data by detecting the amount of past-away based on _2, smooth free-form surface as a whole A product having an outer shape can be obtained.

In the above-described embodiment, a case has been described in which the number of patch divisions is set based on the distance between the midpoints of the diagonal lines connecting the representative points and the sampling points. However, the present invention is not limited to this, and it is not limited to this. The number of patch divisions may be set using the detected excessive shaving amount together.

Further, in the above-described embodiment, a case has been described in which a patch expressed by the Bezier equation is cut into a quadrilateral minute area, and an offset polyhedron is formed based on the data of the vertex positions. The present invention is applicable to the case where an offset polyhedron is formed by calculating a function such as a Bezier equation or a B-spline equation, and the case where an offset polyhedron is formed from a free-form surface represented by a B-spline equation or the like. Even in this case, the same effect as in the above case can be obtained.

H Effects of the Invention As described above, according to the present invention, by detecting the overcut amount based on the distance between the midpoints of the diagonal lines connecting the sampling point and the representative point, the value of the value can be changed according to the surface shape of the patch. The changing amount of excessive shaving can be detected, and the patch is divided based on the detection result to generate offset data, whereby a product having a smooth free-form surface as a whole can be obtained. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the principle of a shaving amount detecting method according to the present invention, FIG. 2 is a flowchart showing the processing procedure, and FIG.
FIGS. 4 and 5 are schematic diagrams showing the difference in the amount of excessive shaving obtained according to the difference in curvature, FIG. 5 is a schematic diagram showing a specific method for detecting the amount of excessive shaving, and FIG. 7 is a schematic diagram for explaining a patch, FIG. 8 is a schematic diagram showing a method for creating offset data, and FIG.
FIG. 10 is a schematic diagram showing a conventional method for detecting an excessive shaving amount, and FIG. 10 is a schematic diagram for explaining the problem. _{A 00 ~A 44, A i ~A} i + 8, A i, j ~A i + 1, j + 1 ...... sampling _{point, B 00 ~B 44, B i} ~B i + 8, B i, j ~B i + 1, _{j + 1}
…… Representative points, E _i , E _{(i, j) 1} , E _{(i, j) 2} , F _i , F
_{(I, j) 1} , F _{(i, j) 2} ... Midpoint, D _i , D _{(i, j) 1} ,
D _{(i, j) 2} ... distance.

Claims (1)

(57) [Claims] 1. A patch forming a free-form surface representing the surface shape of an object is divided to obtain a plurality of sampling points on the patch, and a length method according to a tool to be cut using the free-form surface as a cutting target. An offset data creating method for setting a line vector at the sampling point and creating offset data representing the movement path of the tool based on the position data of the representative point represented by the normal vector. The number of patches is determined based on the distance between the midpoint of the straight line connecting the representative points and the midpoint of the straight line connecting the representative points corresponding to the sampling points. .