JPS63217405A - Production of offset curved surface data - Google Patents

Abstract

PURPOSE:To prevent the excessive cut-off of a processing curved surface due to the blade edge of a tool by interpolating a 2nd tubular offset curved surface and a 3rd offset curved surface for a corner part or a boundary curve that produces a discontinuous space. CONSTITUTION:When a tool moves over a boundary curve that does not satisfy the conditions for continuation of connected planes or a sharp corner part, a 2nd offset curved surfaces COFF12, COFF23 and COFF31 and a 3rd offset curved surface DOFF23 are interplated so that the connection is secured to a 1st offset curved surfaces SOFF1-SOFF3 set opposite to patches S(u,v)1.S(u,v)3 respectively. Thus it is possible to ensure the control so that the tool can pass through a tool route on an offset curved surface formed by said 1st-3rd offset curved surfaces (SOFF1-SOFF3), (COFF12, COFF23, COFF31), (DOFF123). As a result, a cutting process is carried out without cutting off excessively a free curved surface serving as the cutting target when a machine tool is used for cutting.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A: Industrial field of application B: Outline of the invention C: Prior art (Figures 9 and 10) D: Problems to be solved by the invention (Figures 9 to 16) E: Means for solving the problems (Fig. 1 to Fig. 8) F Effect (Fig. 1 to Fig. 8) G Example (Fig. 1 to Fig. 8, Fig. 13 and Fig. 14) H Effect of the invention A Industrial application field The present invention relates to a method for creating offset curved surface data, for example, using computer aided design (CAD) technology.
gn), or CAM (coa+puter aide
This method is suitable for use in creating tool path data for cutting a product having an external shape having the free-form surface using data representing a free-form surface generated in a process such as d a + manufacturing.

B. Summary of the Invention The present invention provides a method for creating offset curved surface data representing the path of a tool across adjacent patches, in which patches or sharp angles are connected under the condition that the condition of tangent plane continuity does not hold in the boundary curve. For patches with
By interpolating the offset curved surface data at the portion where the offset curved surface data is discontinuous with each other, it is possible to control the tool of the machine tool so as not to overcut at the boundary curve position.

C Conventional technology For example, when designing the shape of an object with a free-form surface using a CAD method (geometric n+od
e1ing), designers generally specify 3 that the curved surface should pass through.
By specifying multiple points in a dimensional space (these are called nodes) and having a computer calculate a boundary curve network connecting the specified multiple nodes using a desired vector function, it can be expressed in a so-called wire frame. Create a curved surface. In this way, a large number of framework spaces surrounded by boundary curves can be formed (such processing is called framework processing).

The boundary curve network formed by such framework processing itself represents the rough shape that the designer is trying to design, and a curved surface that can be expressed by a parametric vector function is calculated using interpolation using the boundary curves surrounding each framework space. If it is possible to do so, it is possible to generate a free-form surface (which cannot be defined by a quadratic function) that is designed by the designer as a whole. Here, the curved surfaces stretched across each framework space form basic elements constituting the entire curved surface, and these are called patches.

By the way, in order to give the generated free-form surface a more natural external shape as a whole, it is necessary to create a boundary by placing a patch in the adjacent framework space across the boundary curve such that the boundary curve satisfies the condition of tangent plane continuity. A free-form surface creation method has been proposed in which the control side vectors around the curve are reset (Japanese Patent Application No. 60-277448).

This free-form surface creation method can be used, for example, as shown in Figure 9.
two patches S tut w) + and S (un 1)
! In order to smoothly connect the nodes P(@@), P txo)l , P T33 given by framework processing,
) l % P tox+, P <xs+ t, P
(31)) Based on t, the adjacent patch S (Il
l Vl 1 and S (un vl Z boundary curve cO
Set the control edge vectors a l % a 寞 and C,,c, such that the condition of tangent plane continuity holds in M12, and use these control edge vectors to set the internal control point P(1).
1), P(1□, and P tx, t −, P <Iz□
The principle is to reset the .

This method can be applied to patches S (u, v+ 1 and S
(un Vl l and S (un
vl 2 is smoothly connected to adjacent patches under the condition of tangent plane continuity.

In this specification, a tangential plane means a plane formed by tangent vectors in the U direction and V direction at each point of a boundary curve, for example, the boundary curve C0M12 in FIG.
For each point above, the patch S(., Vl, and S(u
When the tangent planes of +v□ are the same, the condition of tangent plane continuity holds true.

That is, the conditions for tangent plane continuity regarding the point (0, v) on the boundary curve C0M12 are determined as shown in FIG. That is, for patch S (un vl 1,
Direction across the boundary curve C0M12 (i.e. U direction)
The tangent vector H1 of , and the normal vector n of the tangent vector H2 in the direction along the boundary curve C0M12 (that is, the V direction) are n+=HaxHb +・
+++ (1) and patch S (un v)
Regarding Z, the normal vector n2 of the tangent vector Hc in the direction across the boundary curve C0M12 and the tangent vector H1 in the direction along the boundary curve C0M12 is n2=flex Ht,...
...-(2) is expressed.

Under these conditions, for tangent plane continuity, tangent vectors H, , H, and Hc, Hb must exist on the same plane, and as a result, normal vectors n1 and n2
will point in the same direction.

In order to realize this, the internal control point P(IllI ~ P
(tHl and Pil1)2~P, tt, and t may be set, where λ(V), μ(■), and ν(V) are scalar quantities.

In addition, the patch S (un vl l and S(u, v, ! are expressed using a parametric vector function S !u+ vl which is a cubic Bezier 2, as shown in the following equation 5. U and ■ are The U-direction and V-direction parameters E and F are shift operators.

D Problems to be Solved by the Invention Patch 5 (Ill vl) generated in this way
(S (u, vl S(+++ +/l 2) As in (5), the patch S Lu, v) (
An offset curved surface S formed by a surface obtained by moving the position data representing the surface of S (un vl I % S fu+ vl ) by an offset vector F (n).FFI and S.

If vrt is generated, the offset vector F (n
), as shown in Figure 1), patch s1゜1))l
and S (u, vr A function that holds the normal vector n of Z as a variable and is determined by the shape of the tool cutting edge, and the patch S
(+++ IT) l and S,. 5. 】2 is a vector whose starting point is a point on the tool and whose end point is a reference point set in the tool, and the reference point of the tool is the offset curved surface S OF r
(S OF F l, S orrt) When moving over the patch S (unVl (S
It is predetermined to be a function that can move along the surface of TLl+IT)iS (unw)z).

In practice, a 3-axis controlled NC milling machine is configured such that the cutting edge of the tool is directed downward (in the Z-axis direction). For example, if a ball end mill MB with a spherical cutting edge is used as a tool, the offset vector F (n)
As shown in Figure 12, F (n) = Rn...
・It can be expressed as (7), where patch S<LIIV) (S(un
VIIs Contact point C of the cutting edge on S+u+v+t)
A center point O, which is separated by the radius R of the cutting edge in the direction of the normal n from O, is selected as the reference point.

Similarly, tools include flat end mill types with flat tips, and mixed types of ball end mills and flat end mills, each with a patch S(u・VII%5(II・v)2) The distance and direction from the contact point to the reference point is the offset vector F (n)
is predetermined by.

In this way, the offset curved surface S expressed by equations (5) and (6). FFI and S. By inputting the curved surface data of (a) into the control device of the machine tool, the tool can be adjusted so that its reference point is the offset curved surface S. If the cutting edge is controlled to move on the curved surface represented by F, and So, .

Here, as described above with respect to Fig. 1θ, two patches S (,, v) + and S (u
If lwr are connected under the condition of tangent plane continuity, at the position of the boundary curve C0M12, the normal vectors of patches S (un v) l and S (III V□ coincide with each other) , offset curved surface S, , , and S.WF□((5
) and (6) are equal to each other. Therefore, the tool smooths the boundary curve under the same conditions as when cutting the surfaces of patches SIIl+v)I and S(unv□).

The cutting process can be continued while the cutting process is being carried out.

However, as shown in Fig. 13, when two adjacent patches S (un IT) l and S (u, vl t) are connected in a discontinuous state where the condition of tangent plane continuity does not hold at the boundary curve C0M12. Patch S
(Ill vl l and 5(III V) Since the normal vectors of t are not equal to each other, the boundary curve C0
Offset curved surface S at position M12. FFI and S
. There is a problem in that FFt is missing near the position of the boundary curve C0M12, resulting in a discontinuous space (so-called gap) GP12.

In FIG. 13, P. Hl and pcoNz are patch S (un ill + and S (1)1)1 respectively
The control points for cutting out □ to a predetermined size are shown, and the patch S (un vl I and s
(The values of u, vl, are sampled and
The offset curved surface S is obtained by equations (5) and (6). FF
I and S. Position data P OF F + forming Fo
and POFFZ are calculated. Thus, four position data P. An offset polyhedron is formed by connecting a large number of surface elements surrounded by FF1% Porrz, and an offset curved surface S is formed by this offset polyhedron. FFI and S. Fo is represented.

However, in this discontinuous space, the patch s ,...
vl , and S (,,+v) boundary curve C0 of R
There is a risk that the tool that has continued cutting work up to the M12 position may move in an abnormal movement trajectory in the vicinity of the boundary curve C0M12, and if this is left unaddressed, the part of the workpiece on the boundary curve C0M12 may be damaged. There is a risk that the tool will be scraped off (this phenomenon is called tool interference).

In addition to this, as shown in Figure 14, three patches S
(III vl I s S (un vl 2, S
(un vl 3 as boundary curves C0M12, C0M23,
When trying to connect to each other via C0M31, if the condition of tangent plane continuity does not hold in the boundary curves C0M12, C0M23, and C0M31, patch S i
Ll+ ITI 5 (un vl Z, S (III
V) Offset curved surface facing 3 5t) FF1% 5
OFF! , S, , , discontinuous space GP12, GP2
3. Not only GP31 occurs, but also three boundary curves C0
Node P where M12, C0M23, and C0M31 come together
,. , II3 have a sharp corner, a discontinuous space GP123 corresponding to this corner is generated.

Therefore, the patch S llllVII% S turv+t
If the free-form surface formed by SS <unvrs has a sharp corner, tool interference may occur if the tool moves in such a way as to draw an abnormal movement trajectory in the discontinuous space GP123.

``As a method to solve this problem, for example, as shown in FIG. 15, the tool is moved along the path Wl to the first offset curved surface S. 2. When you come to discontinuous space GP12 through
The missing offset curved surface data is detected and the tool is temporarily escaped upward, and while passing through this escape path W2, the tool is
A second offset curved surface S from the offset curved surface S, , , . FF! After that, move the tool across the second offset curved surface S. An easy method would be to move it along the path W3 through the FF.

However, according to this method, for example, as shown in FIG. 16, in which parts corresponding to those in FIG. 15 are given the same reference numerals, the offset curved surface S is created for purposes other than tool movement control. F, and S.

At the position corresponding to the discontinuous space GP12 between FF2, the patch STu・v)I~S(a・v)! If backup data is prepared separately that allows the patch S (un V) X with lower position data to be inserted, the tool will descend to the path W Patch S lu+ vl
I and S (un V) 1 may be accidentally scraped off excessively.

The present invention has been made in consideration of the above points, and even if a discontinuous space occurs between the offset curved surface data, the offset curved surface data can be generated so as not to cause tool interference with the machining shape being cut. This paper attempts to propose a method for creating offset curved surface data that can be easily created.

E Means for Solving Problems In order to solve these problems, in the present invention, sequentially connected patches S (LIIV) 5 (un vl
In an offset curved surface data creation method that generates offset curved surface data representing a tool movement path using a free-form surface formed by Z, S (un w)2 as a cutting target, a patch S (unVIIs S (u+Vl!s S
+IIIVI: first offset curved surface S facing l
. The first data representing FF1% 5OFF□, S, , 3 and the patch S (un vl S (un v)
t, S Tu+ Vl s boundary curve C0M12, C0
A second offset curved surface G having a tubular curved surface formed at a position separated by a predetermined radius from a position on the boundary curve that does not satisfy the tangent plane continuity condition among M23 and C0M31.
. r r + z, to o r F z x, to
second data representing OF y ffI, or the first and second data, and a patch S (un v).
1% S (un vl !, S (u, vl s
] A third offset curved surface having a spherical curved surface formed at a position separated by a predetermined radius from a sharp corner among the corners at the ends of the boundary curves C0M12, C0M23 and C0M31. By creating third data representing F, 23 and interpolating the second data or the second and third data to the first data, a boundary curve that does not satisfy the condition of tangent plane continuity can be obtained. and to form a movement path that does not excessively cut a free-form surface that is a cutting target when the tool crosses a sharp corner.

When the tool moves across a boundary curve or a sharp corner that does not satisfy the condition of continuity of the F action tangent plane, the patch S
V) I % Sfu+ V) t, 5(un V)
1st offset curved surface facing 3OFFI% 5
oryz, S , , , the second offset curved surface Corr+g, COF F Z 3, G
o r r z l and the third offset curved surface D o
By interpolating rFl□3, the first, second, and third offset curved surfaces (SOFFS, ,
,,, S 0FF3), CG OF F + 2
, G OF F t 3, GOFFffl )・ (D
OFFI! The tool can be controlled to move through the tool path on the offset curved surface formed by ff), and thus the machine tool can perform cutting without excessively cutting the free-form surface that is the cutting target .

In this way, it is possible to easily create offset curved surface data representing a tool path that is generated in advance and can be reliably cut into a processed product.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(G1) First Embodiment Figure 1 shows the case of machining with a milling machine using a 3-axis controlled ball end mill. A large number of designed patches S (u
+vl S (u+vl!s S (unv13...
. . . (FIGS. 4 and 5) is read out as necessary, and an interpolation calculation program for offset curved surface data is entered from step SP1.

First, the offset curved surface data creation device performs the following step S.
In P2, patches S , u, V) , S (@* v
Determine the offset IP (n) (formula (7)) of the offset curved surface for 15Tut vl3...

Next, the offset surface data creation device performs step SP3.
, and each patch S (un vl l, S (+a+
vl z, S tu+ vl s... are each cut out into a large number of quadrilateral surface elements, and a first offset curved surface is generated based on the above equations (5) and (6), and this is Offset curved surface 5OFF (5OFFI% 5o
vrz-, 5OFF! ...) is stored in memory.

Next, the offset surface data creation device performs step SP4.
Moving on to the patch S (1) 1) 1) 1% S < ur
w>z, S (MI Vl 3... Based on the data of the boundary curve, the above (1) 2 ~ (
3) Determine whether the condition of tangential plane continuity expressed by the equation holds.

A free-form surface that is actually designed has a large number of patches connected sequentially via boundary curves, and the offset surface data creation device is a process that detects boundary curves for which the condition of tangent plane continuity does not hold for all boundary curves. Execute.

The boundary curve for which this tangent plane continuity condition does not hold is the first
can be calculated based on the above equations (1) and (2), and the adjacent patches S (un vl l and S(u
n V) between 2, S <un vl z and S(un
It is detected when the normal vectors n1 and n2 for the boundary curve between vl, 1, . . . do not match, and secondly, it is detected when there is no patch adjacent to the boundary curve.

In the following step SP5, the offset curved surface data creation device generates a tubular second offset curved surface Gorr (that is, C0F□2 in the case of FIG. 4, and G OF t in the case of FIG. 5) for the boundary curve where the condition of tangent plane continuity does not hold.
t t s COF F t! , G.O.F.F.
z l).

For example, as described above with reference to FIG. 13, two patches S (un v) I and S , , v, are connected under the condition that the condition of tangent plane continuity does not hold at the interface icOM12. 2, the offset curved surface data creation device generates an offset vector F (n) for each point on the boundary curve C0M12 as shown in FIG.
Length IP(n)l (radius R for ball end mill)
Generate a tubular curved surface with a radius of
rrtx).

Thus, the second offset curved surface Corr (=C0t□
2) at any point on the interface 1cOM12, the patch 5(Ill vl I and S (un IT) t
Offset curved surfaces SOF□ and S facing each other. An offset curved surface S connected to FFt. F□ and S. Discontinuous space CP between FF2 is defined by distance IF(n
)l(-R) at a position away from the offset curved surface G
It is possible to interpolate an offset curved surface that is covered by oer (=Govvlt>).

By the way, in practice, a tool consisting of a 3-axis controlled ball end mill is installed from top to bottom in the Z-axis direction, so the second offset curved surface CarF (= Cor
rtz), only the upper half of the tubular curved surface is effectively used. Therefore, as shown in FIG. 3, the offset curved surface data creation device calculates the positions of the cutout points P0 to P4 on the boundary curve C0M12 from the upper semicircle (P@, ~P,,) to (p, ^ ~ P4.)
A tubular curved surface with a semicircular cross section as shown in FIG. 1 is used as the second offset curved surface Gorr (=Corrtx).

Similarly, as described above with respect to FIG.
l 2, S (u, vl 3 is the boundary curve C0M12, C
When data is generated under conditions such that the tangent plane continuity condition does not hold at 0M23 and C0M31, the offset curved surface data creation device generates boundary curves C0M12 and C0.
For each point on M23 and C0M31, the offset vector F (n) length IF (n) I (=R) is the offset curved surface c whose cross section is a semicircular tubular curved surface.
Generate orp.

In the following step SP6, the offset surface data creation device creates the patch S (un Vl 1, S (un '
vl K... Detect sharp corners from the curved surface data.

In this detection process, when multiple boundary curves are gathered at the node at both ends of the boundary curve surrounding each patch, the offset curve data creation device detects the boundary curve that satisfies the condition of tangent plane continuity. If at least one corner exists, it is determined that the corner where the node exists is not sharp. When there is no patch to be connected to the adjacent position, the corner where the node is located is determined to be sharp.

For example, three patches S (u+ Ill l, S
(III Vl t, S (+a, vl s when connected to each other, node P,.) 1) m has three boundary curves C0
M12, C0M23, C0M31 are coming together, but these boundary curves C0M12, C0M23, C0M3
1, the condition of tangent plane continuity is not satisfied in any case, so the offset curved surface data creation device uses the boundary curve C0M12.
, C0M23, and the node P at one end of C0M31.

,l! , is judged to be sharp.

After detecting whether the corner is sharp in this way, the offset curved surface data creation device generates a third offset curved surface DOFF having a spherical curved surface at the sharp corner, as shown in FIG. 6, in the following step SP7. .

This offset curve. 2F is a node P at a sharp corner. 1) Centered on 13 and offset amount I of the tool
It is composed of a spherical surface with a semicircular cross section having a radius of F (n)l (=R).

In this embodiment, the tool is a 3-axis controlled ball end mill, so the third offset curved surface is used. F.

is selected as the hemispherical surface formed by the upper half of the sphere as the range in which the tool can move for machining, and the data of this third offset curved surface DOFF is stored in the memory.

In this way, the offset curved surface data creation device, for example,
As in the case shown in the figure, the first offset curved surface 5OFF ("
5OFFI, 5orvt, 5orts), if there is a discontinuous space CP (=GP12, GP23, GP31) along the boundary curves C0M12, C0M23, C0M31, a tubular second offset curved surface Gorr (=Gorr
+z, Gorrzy, Gorv3+>, and a third spherical offset curve in the discontinuous space GP123 caused by sharp corners, if any. FF
After generating ("DOF□,), in step SP8, these first, second, and third offset curved surfaces 5OFF
A tool path is generated based on % Cart % DOFF, and the processing program is ended in step SP9.

In the above configuration, as shown in FIG.
1) 1VI + and S (u, vl t boundary curve C0
Since M12 is connected in a state where the condition of tangent plane continuity does not hold, the patch S (u + VI and S (
Offset curved surface S facing u, □2. FFI and S.

When there is a discontinuous space CP (=CI' 12) between FF1, the offset curved surface data creation device creates a second tubular offset curved surface C0F formed around the boundary curve C0M12 in the discontinuous space GP (=GP12). .

(=C, , , □) is interpolated.

At this time, the tubular offset curved surface G. rr (=Gotxt
＞ is a discontinuous space GP (=GP
12), patches S , , V) and S (141VI
Offset curved surface S facing Z. FFI and S. F2
□Can be connected between.

Here, the offset curved surface data creation device generates patches S, , V) of the second offset curved surface C0FFI2.
, and S (Il, the offset curved surface So facing ill z, , and S.2o are selectively processed so that they are not used as offset curved surfaces, and the offset curved surface S.2F that is generated in this way is S.O.
F. , C0, □2, only the curved surface portion having the outermost position data is selected to obtain an offset curved surface representing the movement path of the tool.

(Then, while the tool is machining patch 5 (IJI V) 1, the boundary curve C0M1 where the condition of tangent plane continuity does not hold)
When it reaches position 2, it is controlled to move on the offset curved surface C0FFiffi interpolated to cover the discontinuous space GP12, and then moves onto the offset curved surface s orvt facing the patch S(...)2. do.

Therefore, when the tool crosses the discontinuous space GP12, the cutting edge does not fall deeper than the boundary curve C0M12, so the boundary curve C does not satisfy the condition of tangent plane continuity.
Two patch S + v) I connected by 0M12
and S (un v, t) can be cut with just the right amount.

In addition, the offset curved surface data creation device performs step SP8.
In, as shown in FIG. 5, three patches S (u
n v) 1% S (ul vl!, S (ul
V) When cutting a free-form surface formed by connecting 2 in such a way that the condition of tangential plane continuity does not hold, the offset curved surface facing these patches 5OFFI% 5oyyts
Discontinuous space GP12, CP23 that occurs between 5OFF3
, GP31 respectively as the second offset curved surface C0FFI
Z, G o F F z 3% G o F F 3
Interpolate by 1.

In addition to this, there are three patches S (un vl l s
S (ul vl is.

The node P(.,
1.3 forms a sharp corner as described above with reference to FIG. 14, and this corner is interpolated by the third offset curved surface DOFFI23.

In this case, the offset curved surface data creation device generates a tubular second offset curved surface G or F as shown in FIG.
l! % G o r r z x , G o r
F21 and spherical third offset curved surface DOFF1
! 3 and Patch S(u・VII%S(ul vl z
, S (first offset curved surface S facing Ill V13. F6.5oFF!, S, , , , select only the outermost offset curved surface to determine the tool movement locus, that is, the tool path as a whole. An offset curved surface can be formed as a whole.

According to the above configuration, for the boundary curve of each patch forming the free-form surface that is the processing target, for the boundary curve where the condition of tangent plane continuity does not hold, the tubular offset curved surface C
By interpolating 0FF and also interpolating the spherical offset curved surface DOFF when the end corner of the boundary curve is sharp, the tool can be moved relative to the free-form surface that is the machining target. When attempting to perform cutting using a cutting tool, when moving the tool across the boundary curve after finishing machining on one patch, the cutting edge moves abnormally, causing the cutting edge to excessively cut down the boundary curve of the target patch. It is possible to easily form a tool path that can prevent the risk of damage.

(G2) Other embodiments (1) In the above embodiment, processing was carried out using a milling machine using a 3-axis controlled tool with the tool attached so that the cutting edge faced downward in the Z direction. Although an example has been described, the tool is not limited to this. For example, the same effect as described above can be obtained even if the tool is used in a milling machine that uses a tool configured such that the direction of the cutting edge can be changed arbitrarily.

(2) In the above embodiment, for boundary curves that are connected without satisfying the tangent plane continuity condition,
Tubular second offset curved surface C6FF (G or
F I z , G O F r Z 3 , G or
r 31 ) and a spherical third offset curved surface at the sharp corner. When forming FF (DOFF+23), considering that the tool of the 3-axis controlled ball end mill is installed from above to below in the Z direction, the tubular offset curved surfaces C0, F and the spherical offset curved surface are formed.

The lower half of the FF is not actually used to form the tool path, so we have discussed the case where it is omitted, but it is also possible to create a machine tool in which the direction of the cutting edge can be changed arbitrarily. When used, a cylindrical curved surface with a circular cross section is generated as the second offset curved surface, and a cylindrical curved surface with a circular cross section is generated as the third offset curved surface, but the same effect as in the above case can be obtained. Obtainable.

(3) In the above embodiment, an example was described in which processing was performed using a milling machine that uses a ball end mill with a spherical cutting edge, but the tool is not limited to this. For example, a flat end mill with a flat cutting edge or a cutting edge Various types of tools can be used, such as a tool with a combination shape of a ball end mill and a flat end mill, and in this case, the offset vector F ( n) is selected based on the shape of the tool, the offset curved surface S. By interpolating the second and third offset curved surfaces C8□ and DOFF with respect to FF, it is possible to effectively prevent the possibility that the cutting edge of the tool will perform an abnormal operation such as excessively cutting the cutting target.

(4) In the above embodiment, the first offset curved surface S. F4, second and third offset curved surfaces C0FF
and D04. We have described the case where the polyhedron is cut out into quadrilateral plane elements of a predetermined size and an offset polyhedron is formed based on the data of the vertex positions. Even if it is formed by calculating , the same effect as in the above case can be obtained.

Effects of the Invention As described above, according to the present invention, the movement path of the tool is set using the first offset curved surface formed to face the patch constituting the free-form surface that is the machining target. By interpolating the tubular second offset curved surface and the spherical third offset curved surface for boundary curves or corners where a discontinuous space occurs, the cutting edge of the tool does not excessively scrape off the machined curved surface. Furthermore, offset curved surface data that can effectively prevent this can be easily created.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the method for creating offset curved surface data according to the present invention, and FIGS. 2 and 3 are route maps showing a method for generating a tubular offset curved surface that interpolates discontinuous spaces generated in boundary curves. , FIGS. 4 and 5 are route maps showing an offset curved surface interpolated by a tubular offset curved surface and a spherical offset curved surface, FIG. 6 is a route map showing a spherical offset curved surface for a sharp corner, and FIGS. Figure 8 is a route map for explaining how to select an offset curved surface, Figure 9 is a route map for explaining a boundary curve connecting two patches, and Figure 1O is a vector diagram for explaining the conditions for continuity of the tangent plane. , 1) Figure 1) is a vector diagram for explaining the offset vector, Figure 12 is a route diagram for explaining the movement trajectory of the tool, and Figures 13 and 14 are route diagrams for showing the discontinuous space that occurs between the offset curved surfaces. , FIG. 15, and FIG. 16 are route maps for explaining the movement path of the tool. S+u+ vl ,5(ll+ vl l,S(u+
Vl z, S (1) 1V) , ... patch, CP, C; Pi-Gl) 3 ... discontinuous space,
5OFF, 5ort 5OFF! , 5o412.・・・
...First offset curved surface, Co y F , C
OF r I2 % G o r y Z 3, COF
r 3 +...Second offset [curved surface, D
,,,. DOFFI23...Third offset curved surface.

Claims (2)

[Claims] (1) In an offset curved surface data creation method that generates offset curved surface data representing a movement path of a tool using a free-form surface formed by sequentially connected patches as a cutting target, a first offset curved surface facing the patch is representing the first
and a second offset curved surface having a tubular curved surface formed at a position separated by a predetermined radius from a position on the boundary curve of the patch that does not satisfy the tangent plane continuity condition. By interpolating the second data with respect to the first data, the above data becomes the cutting target when the tool crosses a boundary curve that does not satisfy the tangent plane continuity condition. A method for creating offset curved surface data, characterized by forming a movement path that does not excessively cut a free-formed surface. (2) In an offset curved surface data creation method that generates offset curved surface data representing a movement path of a tool using a free-form surface formed by sequentially connected patches as a cutting target, a first offset curved surface facing the patch is representing the first
and a second offset curved surface having a tubular curved surface formed at a position separated by a predetermined radius from a position on the boundary curve of the patch that does not satisfy the tangent plane continuity condition. 2, and a third data having a spherical curved surface formed at a position separated by a predetermined radius from a sharp corner among the corners at the end of the boundary curve of the patch.
By interpolating the second and third data with respect to the first data, the boundary curve and the peak that do not satisfy the tangent plane continuity condition are A method for creating offset curved surface data, comprising forming a movement path that does not excessively cut the free-form surface, which is a cutting target, when the tool crosses the corner of the vine.