JPS6364109A - Processing information generating system for free curved surface removing tool interference - Google Patents

Abstract

PURPOSE:To generate tool path data to satisfy a processing accuracy at a high speed by generating an off-setting polyhedron from a three-dimensional free curved surface and selecting necessary X coordinate of a picture element corresponding to the intersection of a lattice on XY coordinate plane. CONSTITUTION:A three-dimensional free curved surface from an input device 4 is divided for a picture element for cutting by a free curved surface generating system 1, and a polyhedron off-set from a free curved surface is generated in accordance with a tool shape. Based on the polyhedron, a tool path generating system 2 for cutting curved surface calculates a Z coordinate value corresponding to respective intersection coordinates of a lattice set at the prescribed interval on a plane in a projection graphic to the XY coordinate plane of respective picture elements. The maximum value out of plural Z coordinate values to belong to the same intersection is selected and a tool path is obtained by corresponding to the XY coordinates. Thus, the interference and non-interference of a tool are decided, and tool path data to satisfy a necessary processing accuracy can be generated based on a sufficient data quantity at a high speed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is an NC machining machine that uses a three-dimensional free-form surface. [Summary of the Invention] When generating tool path data for a numerically controlled machine tool from data of a three-dimensional free-form surface Next, a polyhedral response consisting of surface elements for cutting is performed, the surface elements are extracted one by one, and the Z coordinates of the surface elements are obtained at grid-like sampling points on the XY plane limited within that plane, and the same sampling point is This system is characterized by eliminating tool interference by taking the maximum value when there are multiple Z coordinates and using it as tool path data.This system improves data generation efficiency and enables high-speed processing. be.

[Conventional technology]

A CAD/CAM system that handles three-dimensional free-form surface data inside a computer and generates NC data (tool path data) for automatically machining final products or molds using NC machine tools, etc. is now in practical use. It is becoming more and more popular.

One of the conventionally known methods of tool path generation is APT (Auto + naturally Pro).
There is a grammed tool). The main body of APT is a general-purpose automatic programming language for multi-axis contour control with a writing style similar to English. This language contains instructions regarding the geometry of the workpiece and tool, the movement of the tool relative to the workpiece, the functionality of the machine tool, tolerances, arithmetic calculations, etc.
Contains definitions. When a program written in this language is run on a large computer, it is possible to output NC tape.

On the other hand, when handling curved surfaces such as the outer diameter of a product in a computer, the Bezier formula or B-3pline has favorable properties for design such as good shape controllability (easy deformation and modification) and easy calculation. Parametric and metric expressions using formulas are often used.

[Problem that the invention seeks to solve]

The most fundamental problems inherent in tool path generation are the problem of data generation efficiency considering machining accuracy and the problem of tool interference determination.

In the APT described above, the user instructs (programs) the tool forward path, and as a result, cutting data for a free-form surface is generated, and the tool path is automatically generated from the geometric model generated within the computer. isn't it. Originally CAD/
The CAM system improves overall efficiency by transmitting shape information during design to processing, and APT
Design is done separately, and efficiency cannot be improved if the tool path for machining is programmed with the required shape in mind.

On the other hand, a parametrically expressed curved surface is convenient for shape definition because it does not depend on the coordinate system.

However, since the coordinate system of machine tools that cut curved surfaces is fixed, machining data (
(Tool path data) cannot be converted with high accuracy.

For this reason, machining accuracy decreases.

In addition, when directly cutting based on parametric expression,
It is technically difficult to check for interference (collision) between the tool or tool holder and the finished shape, resulting in the inconvenience of cutting off the necessary portion.

In other known methods of surface representation using polyhedral approximation, sufficient machining accuracy cannot be obtained unless a huge amount of data that exceeds the processing capacity is handled. Therefore, it is impossible to expect to generate processing data in a short time that is practical. If the number of data representing the curved surface is reduced in order to perform high-speed processing, the processing accuracy will become rough, making it impossible to satisfy the designed tolerance of the curved surface.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to generate tool path data that satisfies required machining accuracy at high speed while determining tool interference and non-interference.

[Means for solving problems]

The present invention processes data representing a three-dimensional free-form surface to
This is a system that generates tool path data for a numerically controlled machine tool that controls at least three axes, such as a C-milling machine.

A means is provided for dividing the free-form surface into cutting surface elements and generating an offset polyhedron offset from the free-form surface according to the shape of the tool.

In the projected figure of each surface element above on the XY coordinate plane,
Means is provided for calculating the Z-axis coordinate value of a point on the plane element corresponding to each intersection of a grid set at predetermined intervals on the XY coordinate plane.

Means for selecting the maximum value of the plurality of Z-axis coordinate values belonging to the same intersection point and storing it in correspondence with the XY coordinates of the intersection point (
memory).

The apparatus further includes means for generating tool path data for controlling the tool in the three axes of XYZ based on the contents stored in the storage means.

[Effect]

This is a tool path generation system most suitable for 3-axis numerically controlled machine tools with an orthogonal coordinate system (XYZ axes), and performs tool interference removal processing at high speed in an orthogonal coordinate system.

The process of generating an offset polyhedron and the process of calculating the tool path from the offset polyhedron are separated, and the tool path is calculated using an orthogonal coordinate system, but the generation of the offset polyhedron uses Bezier surface, B-5pline surface, Co
It can be based on a representation format of a geometric surface such as an ons surface. Therefore, it is possible to process a wide variety of curved surfaces without depending on the data structure of the curved surface representation.

Furthermore, even if the workpiece is composed of multiple curved surfaces, it can be handled in the same way as a single curved surface.

Since the tool path is converted into the form of Z coordinate values at lattice points on the XY coordinate plane, various tool paths along scan lines, equal straight lines, etc. can be set according to the curved surface.

Furthermore, tool interference removal processing is performed only once on one of the surface elements constituting the offset polyhedron, and no redundant calculation processing occurs, so tool path data can be generated efficiently and at high speed.

〔Example〕

<C. Overall configuration of the system> FIG. 1 shows the overall configuration of the CAD/CAM system of the embodiment. In FIG. 1, the free-form surface generation processing system 1 is
In the part corresponding to CAD, shape data of a geometric model expressing the three-dimensional free-form surface of the object is generated based on input operations by an operator, and is stored in a file. The objects are machined parts and molds.

The generated shape data is converted into machining data, that is, data for determining the movement path of the cutting tool, in the free-form surface cutting tool path generation system 2.

The processing data is downloaded to a floppy disk, and automatic processing is performed by loading the floppy disk into the NC milling machine 3 (NC milling machine or machining center).

The free-form surface generation processing system 1 and the free-form surface cutting tool path system 2 are actually computers, and are attached with an input device 4 such as a keyboard or a digitizer, and a display device 5 such as a CRT for a user interface.

The tool path generation system 2 takes into account (1) the shape accuracy of the free-form surface (2), the surface roughness of the free-form surface (3), and tool interference check, and generates machining data at high speed. It works with a devised algorithm.

G2: Configuration of tool path generation system> As shown in FIG. 2, the tool path generation system includes a plurality of program modules that are activated sequentially or in parallel. Each program module can be thought of as a dedicated data processor and will therefore be referred to hereinafter as a processor.

First, the accuracy determination preprocessor 21 and the surface roughness determination preprocessor 22 are activated in the preliminary processing stage.

The precision determination preprocessor 21 determines the division fineness for dividing the curved surface of the geometric model generated in the CAD stage into a large number of quadrilaterals (or triangles) based on the tolerance specified for the target workpiece. decide. With this polyhedral division,
Cutting shapes (cutting models) that are approximated within tolerances can be generated. By polyhedral approximation that takes tolerances into consideration, it is possible to determine an optimal tool path for performing cutting that is not unnecessarily highly accurate and satisfies design specifications.

When the error between the radius of curvature ρ of the geometric surface and the distance from its center to the approximate polyhedron is δ, the size of each side of the approximate polyhedron is determined so that δ according to equation 1 is within the specified tolerance! , the finishing accuracy preprocessor 21 determines the sampling width on the hanging geometric model curved surface.

The tool path is set on the generated polyhedron.

In other words, the tool cuts a curved surface while moving minutely in a straight line from point to point in space. Such cutting processing can be realized with a normal three-axis controlled NC milling machine.

Note that the actual tool path is set on a virtual offset polyhedron offset from the cutting edge of the tool to the tool center (command position W for tool movement) with respect to the machining surface.

Next, the surface roughness determination preprocessor 22 determines the feed width (feed pinch) of the tool based on the surface roughness specified for the target workpiece. Generally, if the tool feed width is narrow,
The surface is cut more smoothly. However, if the time during tool feeding is reduced to 1/2, the amount of data defining the tool path will double. Therefore, the tool feed width must be set optimally to obtain the required finished surface roughness with minimum tool path data. The surface roughness determination preprocessor 22 includes an algorithm for calculating a tool feed width that satisfies a given surface roughness.

When using a ball end mill as a (radius R) cutting tool, the surface roughness determination preprocessor 22 determines the roughness so that the height H of the amount of uncut material on the machined surface satisfies the specified surface roughness.
Determine the tool feed width Δ using the formula %.

The data on the division fineness of the offset polyhedron and the tool feed pitch obtained by the accuracy determination preprocessor 21 and the surface roughness determination preprocessor 22 are passed to a tool path generation processor consisting of a rough cutting processor 23 and a finishing processor 24. , based on these, the curved surface data of the geometric model is sequentially processed to finally generate tool path data. Note that rough machining and finish machining differ only in the size of the tool, the feed width, and the presence or absence of a finishing allowance, and the data processing algorithm can be considered to be the same. Additionally, tolerances and surface roughness do not need to be considered during the rough cutting process.

The most important function of these tool path generation processors 23, 24 is to determine a tool path that avoids tool interference. Tool interference is most likely to occur during rough cutting processes where the outside diameter of the tool is large. Furthermore, by devising the tool path generation algorithm, these processors 23 and 24 can generate tool paths at high speed.

The generated tool path data is sent to the NC milling machine 3 shown in FIG. 1 using a floppy disk or the like as a medium in the order of rough cutting and finishing, and milling is performed on the block material.

Note that the tool path generation system shown in FIG. 2 is attached with a parameter cutting processor 25, and it is also possible to directly perform cutting based on the original curved surface shape data expressed in parameters. Although this processor 25 does not perform a tool interference check, for curved surfaces for which it is predicted that no interference will occur, parameter cutting can be selected depending on the shape of the curved surface.

Furthermore, the tool path generation system includes a tool path display processor 26 and an interference location display processor 27. By displaying three-dimensional images by these processors, tool paths and tool interference can be visually recognized.

Each processor or preprocessor of the tool path generation system can communicate data to and from input/output equipment through the user interface module 28.

Operators operate each processor using input/output devices such as keyboards, displays, and XY plotters.
Processing results can be obtained.

FIG. 3 shows a processing flowchart of the tool path generation system of FIG. 2. First, curved surface data is read from a computer file (input PL). Next, the curved surface data is displayed and the data is confirmed (display P2). Next, proceed to the roughing process,
Generates a tool path for rough cutting. In the rough cutting process, first, the finishing allowance and tool diameter are specified (operation P3). Based on these specified values and the curved surface data, the rough cutting processor 23 (routine P4) generates a tool path that avoids tool interference. Using the data generated, the rough cutting tool path, cutting start point, and cutting end point are displayed (display P
5) If there is an unavoidable tool interference location at this time, it is displayed (display P6).

If tool interference occurs (judgment P7), the process returns to operation P3 to change the tool diameter and generates the tool path again.

If it is determined in determination P7 that there is no tool interference, the process proceeds to the next finishing process. In this process, first, the finishing tool diameter is specified (operation P8). Furthermore, the tolerance class (allowable tolerance) of the registered general tolerance table is specified (operation P9). Next, the preprocessor 21 (
The finishing accuracy (fineness of division into offset polyhedrons) is determined by starting the routine PIO) and comparing the specified tolerance table with the cutting dimensions. Furthermore, the surface roughness value specified in the design drawing is input (operation P11). Based on this specified surface roughness value, the tool feed width is determined by the finished surface roughness determination preprocessor 22 (routine P12).

Next, the finishing milling processor 24 (routine P13) is activated to generate a finishing milling tool path based on the polyhedral division fineness and tool feed width data determined by the allowable tolerance and designated surface roughness.

Using the generated tool path data, the tool path for finishing cutting is displayed, and the tool interference location is also displayed (display P14, PI3). Change the finishing tool path and generate the tool path again. If the interference is removed by this tool change, the generated tool path data is written to a file and the series of processes ends.

G3: Basic concept of tool path generation process> The tool path generation process, which consists of the rough cutting processor 23 and the finish cutting processor 24, basically generates an offset polyhedron from the curved surface data of the geometric model, and then calculates tool interference from this polyhedron. This is a procedure for quickly generating tool path data without

When cutting point A of the free-form surface S with the ball end mill 10 as shown in FIG. 4, point A becomes the contact point between the free-form surface and the blade surface of the ball end mill. In this case, ball end mill 1
The vector AO connecting the center O of the sphere of 0 and the point A becomes the normal vector at the point A of the free-form surface. This vector is called an offset vector.

-m indicates that the offset vector at a point on a curved surface is a vector that starts from that point and ends at the reference point set in the tool when the tool is brought into contact to cut that point. . Vector F is generally a function F (n) of normal vector n.

In the case of a ball end mill, F (n) = rH (r is the radius of the spherical part).

Considering offset vectors at all points on a free-form surface, the end points form one curved surface. If this curved surface is called an offset curved surface, the desired free-formed surface can be machined by moving the tool so that the center of the tool is clearly on the offset curved surface.

The simplest method for generating a tool path based on an offset curved surface is to consider a sequence of points to be cut on a free-form surface, and to define the end point of the offset vector at each point as the sequence as the tool path. This method is mainly used for free-form surfaces expressed by parametric equations.

For example, consider a free-form surface expressed parametrically as shown in FIG. The position fP (X, t, 2) of a point on the surface is given as the period of the parameter usV by x=f,' (u, v) y=fz (u, v) z=f3 (u, v) . In such a curved surface, t2. If v is given, the points on the curved surface and the normal direction can be easily found, so by changing u and v, create a point sequence (A) as shown in Figure 6,
A corresponding point sequence (0) at the center of the tool can be obtained as the tool path.

Another method, as shown in FIG. 7, is to generate a corresponding offset curved surface from a free-form surface and to generate a tool path by parametrically specifying points on the offset curved surface. For example, if the free-form surface is expressed by the following formula, x” g + (u, V)
-Cth u' + CI 2 u'' V +c, 3u
v” +c, 4v3+c15u” +c,, uv+c,
,v'' +c, ,u+c,,v+c,A)'=gz(u
, v)=c2. u” +c, 2u”v+C23uV”
+c, 4v3 +c,,u” +czhuv+c
2. v” +c2su+c,,v+ctAz=g,(
u, v)=c3. u' +C=zu” V+C33
u v" + C34V' + c3su"
+ (34u v+ G3.v” + c,
, u + c, qv + c3^ Point P of free-form surface points 10
Consider an offset vector between 1 and P1°, and find its end point Q
An offset curved surface can be obtained as a curved surface passing through , ~Q1°. In this offset curved surface, a tool path can be generated by changing parameters U' and V'.

The tool path generation method described above does not take tool interference into consideration. For example, if an attempt is made to cut part A as shown in FIGS. 8a and 8b, a necessary part in the vicinity thereof will be cut off. This is tool interference caused by the tool shape. Alternatively, as shown in FIG. 9, unless the angle of the ball end mill is changed, there may be cases where it is impossible to avoid tool interference and cut part A. This is tool interference caused by the setting conditions of the machining axis.

To find tool interference, you can calculate the intersection of the ball end mill and the target free-form surface, but it takes a lot of calculation time to obtain a certain degree of accuracy, so tool interference is actually detected. The tool path is generated while being checked by humans to ensure that this does not occur.

In order to solve such a tool interference problem, a verification method in the Z-axis direction as shown in FIG. 10 can be used. In this method, the axis of the ball end mill is set in the Z-axis direction, a straight line 2 parallel to the Z-axis is considered, and the intersection of this line and the offset curved surface is determined. When tool interference occurs, the tool path on the offset curved surface draws a loop as shown in the figure, so a plurality of intersection points H+, H2, and H3 are found for one straight line yA'.

A point H3 having the largest value (height) in the Z-axis direction of these intersection points becomes a point on the offset surface where tool interference is avoided. Such an offset curved surface is x of straight line l,
It is expressed by the y coordinate and the two coordinates of the intersection.

G4: Specific example of tool path generation process> A specific tool path generation process based on the above-mentioned principle basically consists of the following steps.

First step: Generate an offset polyhedron from the free-form surface.

Second step: Find the highest position of the offset curved surface at a point on the XY plane.

The second step algorithm is the ``lattice point height method,'' which specifies schools of fish on the XY plane using lattice points and calculates the Z axis.
are detailed below.

Figure 11 shows the characteristics of this algorithm. The offset curved surface is a polyhedron. A school of fish is arranged in a lattice pattern on the curved surface of the target geometric model, and the offset vector (normal vector in the case of a ball end mill) at each point is calculated to find the lattice points on the offset curved surface. Lattice (quadrilateral)
By dividing each one into two triangles, an offset polyhedron is obtained. In the part where there is tool interference, the offset polyhedra overlap in the Z-axis direction, as shown in the 11th view.

Next, an orthogonal coordinate system is taken in which the tool axis of the NC milling machine is the Z axis. The XY plane becomes a horizontal plane. A grid point group (X8, y,) is given on the XY plane, and the height of the offset polyhedron corresponding to each point is determined. This problem can be easily solved as a problem of finding a solution (intersection point) between a straight line parallel to the Z axis passing through a lattice point on the XY plane and one triangle of an offset polyhedron. Height 22 of the obtained offset polyhedron
．． By selecting the higher value of 2□, tool interference can be avoided. The tool path is set on an offset polyhedron.

FIG. 12 shows the processing procedure of the lattice point height method.

Step 1 (Figure 13) Find the normal vector n at the grid point on the geometric model surface. Each grid point (sample point) is obtained by arranging the grid points on the curved surface in a grid pattern so as to satisfy the required tolerance based on the result (sampling interval β) of the accuracy determination preprocessor 21 described above. The lattice spacing, that is, the fineness of division into polyhedrons, is determined by the curvature of each curved surface and the specified tolerance class.

Note that FIG. 13 shows a patch of plane elements constituting a geometric model, which is expressed parametrically by 16 control points. When this patch is subdivided into a grid, the results from the precision determining preprocessor 21 are used to perform division so that the final finished shape falls within the tolerance.

Step 2 (14th N) Obtain an offset vector F from the normal vector n at each point. The function F (n) is determined by the tool shape.

Step 3 (FIG. 15) Divide each quadrilateral on the offset curved surface determined by the end point of the offset vector into two to obtain an offset polyhedron whose surface elements are triangles.

Step 4 (Fig. 16) Pick out one triangle constituting the offset polyhedron and find the equation of the plane passing through its three vertices.

z = C1x + C2y + C3 Step 5 (Figure 17) Consider a grid point (i, j) on the XY plane, and calculate the coordinates of that point (
xi j, yth), X1j=i ・Δ+xc yLj”J ・Δ+y.

Defined by. (Xc,,yc) are the coordinates of the fixed point, and Δ is the grid spacing.

Δ is set by the previously described surface roughness determination preprocessor 22 to a value equal to or less than the tool feed width calculated from the surface roughness designation given at the time of design.

Here, prepare a memory array called z (i, j),
Assign the height of the triangle in the Z-axis direction at point (i, j) to a storage location.

Step 6 (FIG. 18) Consider the orthogonal projection of a triangle onto the XY plane, and limit the lattice points on the XY plane that correspond to the triangle. This school of fish is a straight line parallel to the X and Y axes passing through the vertices of the triangle x1%in,
X, )'ai+s, Vw*ax (dotted line in FIG. 18) can be limited to the inside of the rectangle.

Step 7 (19th') It is determined whether the fish school (i, j) limited in Step 6 is included within the orthogonal projection of the triangle. For example, the point (xij,)'(j) is the straight line'g (x
Regarding i,,y+) ~(x2,)'z),
It is sufficient to determine whether or not the point is on the same side as the point (X3,)'i), and do the same for the other two sides of the triangle.

The equation that matches one side of the triangle is ()')'1) (x* x,) - ()'!
)'l) (X-XI) =0. F on the left side
(x, y), F(Xtj, y, J) and F (X
3,)'3) have the same sign, the point (X84, y
Lj) and point (xi,)! 3) can be determined to be on the same side. The same process is performed on the straight line (Xz,) l'z) ~ (x3
, ys), the straight line (Xi, Vs) to (X,, yl), and the points (Xaj, Xtj) are respectively
)'+), (Xi,)'! ) on the same side as
It can be determined that the point (xijs y□,) is inside the triangle.

Step 8 Using the equation passing through the three vertices of the triangle obtained in Step 4, find the height Xtj on the surface of the triangle at the point (xijs yij).

z; J = C1X = j” Cty+ j”
C3 Step 9 Compare the previous value in the memory array z (1% J) with the new zij found in step 8, and z ij > z
(1% J), replace the memory value with Zij. It is thought that tool interference has occurred in the part where replacement has occurred. This process leaves a high offset polyhedron with respect to the Z axis and removes tool interference.

Step 10 (Figure 20) z (i, j
) is on the offset polyhedron, and its orthogonal projection matches the lattice points on the XY plane, so the tool path can be easily generated from the memory array. For example, as shown in FIG. 20, continuous scanning is performed in the i direction, and
A tool path is generated by step feeding in the direction.

Actually, the address pointer i in the memory is increased while the tool of the three-wheeled milling machine is continuously moved (scanned) in the X-axis direction. Every time one section of scanning is completed, the tool is moved in the Y-axis direction by Δ and the address pointer j is incremented by one. The tool control in the Z-axis direction is read from memory by the address (i,j) (direction z
In order to shorten the machining time performed at (j, j), it is preferable to perform the tool movement on the X axis in a reciprocating manner as shown in FIG.

Note that it is also possible to generate tool paths not only along scan lines but also along equal straight lines.

Method 1: R is a fake The tool path can be generated at high speed using the ``lattice point height method'' explained above.

In general, generating a tool path without tool interference can be considered as a problem of finding an outer curved surface in the Z-axis direction of an offset curved surface, as shown in FIG. To obtain the outer envelope curved surface, the heights 21 (offset curved surface 1) and zz (offset curved surface 2) of the curved surface at the same -x, y coordinates may be determined and compared in size. However, tactilely, the offset curved surface is expressed in a parametric form as shown below.

X-value φ, (u, v) y=φt (ulv) 2=φ3 (uSV) Therefore, to obtain 2 from x and y, a convergence calculation that requires repeated operations must be used, and there are multiple curved surfaces. If it exists, a curved surface passing through the point (x, y) must be searched from the set of all curved surfaces. Therefore, a huge amount of calculation must be performed.

There is also a method of approximating a parametrically expressed offset surface with a polyhedron. For example, in Figure 22, off-site/
) The curved surface is approximated by a polyhedron consisting of planes 31 to S7. 31 to S7 can be expressed by a linear equation (7). This formula can be easily converted into z = f i
Since it can be transformed into the form (x −, y), if you search that surface S4 includes the position (x, y), you can calculate z without repeating the calculation.
You can find the value.

This method (lattice point height method) is characterized in that it does not even search for surfaces. Therefore, the position (x, y) is the grid (G
An array z (i, j) with a height on the grid is prepared.

Then, as shown in FIG. 23, planes Si are sequentially selected from the offset polyhedron U, and the corresponding positions (i, j
) and write it to array 2(i,j) to line ((steps 4-8).

In this method, there is no need to search for the plane Si located on the point (x, y) in all the offset polyhedra.

Therefore, the total number of faces Si of the offset polyhedron can be processed at high speed on the order of n.

On the other hand, when searching for a triangle corresponding to the position of one point on a certain xy plane, it is necessary to process a total number mxn, where m is the number of corresponding triangles.

In order to avoid this overhead, in the past, it was necessary to take measures such as reducing the number of polyhedra to be processed.
Decreasing machining accuracy was a problem.

〔Effect of the invention〕

As described above, the present invention separates the process of approximating a geometric surface with an offset polyhedron and the process of generating a tool path from an offset polyhedron, so that the process of approximating a geometric surface with an offset polyhedron and the process of generating a tool path from an offset polyhedron are performed. Tool path data can be generated.

Since tool interference removal processing is performed only once for each surface element constituting the offcent polyhedron, and no duplicate calculation processing occurs, tool path generation is efficient and high-speed processing is possible.

Since the tool path is in the Z (i, j) format corresponding to the grid points of the XY coordinates, a convenient tool path such as a scan line or equilinear line can be determined.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the overall configuration of a CAD/CAM system showing an embodiment of the tool path generation system of the present invention, and FIG.
The figure is a block diagram of the tool path generation system, and FIG. 3 is a flowchart of the data processing procedure of the tool path generation system. Fig. 4 is a diagram showing the relationship between the confessional surface and the offset curved surface, Fig. 5 is a diagram showing the free-form surface in parametric expression,
Fig. 6 is a diagram showing one method of generating a tool path from a free-form surface, Fig. 7 is a diagram showing one method of generating a tool path from an off-set curved surface, and Fig. 8 is a diagram showing a method of generating a tool path from a free-form surface. FIG. 9 is a cross-sectional view showing tool interference caused by the setting conditions of the machining axis, and FIG. 10 is a cross-sectional view showing a tool interference verification method. FIG. 11 is a diagram of an offset polyhedron showing the characteristics of the algorithm of the "lattice point height method", and FIG. 12 is a flowchart showing the processing procedure of the lattice point height method. 13 is a diagram of the geometric surface corresponding to step 1 of the flowchart in FIG. 12, FIG. 14 is a diagram of the offset vector corresponding to step 2, and FIG. 15 is a diagram of the offset vector corresponding to step 3. Figure 16 is a diagram of the triangle (area element) corresponding to step 4, Figure 17 is a diagram of the lattice point array on the XY plane corresponding to step 5, and Figure 18 is a diagram of the lattice point arrangement on the XY plane corresponding to step 6. Figure 19 is a diagram showing the relationship between the triangular surface elements and grid points, Figure 19 is a diagram showing the method for specifying grid points inside the triangle corresponding to step 7, and Figure 20 is a line of the tool path corresponding to step 10. It is a diagram. Fig. 21 is a diagram showing the envelope curved surface of the offset curved surface that avoids tool interference, and Fig. 22 is a diagram showing the envelope curved surface of the offset curved surface that avoids tool interference.
FIG. 23 is a diagram showing an outline of the procedure of the lattice point height method. In addition, in the symbols used in the drawings, 1.-------.--.--Free-form surface generation processing system 2--..--..--.For free-form surface cutting Tool path generation system 3・・・−・・・・・・・NC Me IJ song sing 4・・・−・−・−−−−−1・・・・Input device 5・・・・−・−・−・・〜Display 21−・−
・・・・・・−・Accuracy determination preprocessor 22 ・・−
・・・−・・・−・−Surface roughness determination preprocessor 23−
−−−−・−・−・−・Rough cutting processor 24～・・
...------This is a finishing milling processor.

Claims (1)

[Claims] A system for processing data representing a three-dimensional free-form surface to generate tool path data for a numerically controlled machine tool with at least three-axis control, which divides the free-form surface into cutting surface elements. and means for generating an offset polyhedron offset from the free-form surface according to the shape of the tool, and within the projection figure of each surface element onto the XY coordinate plane,
means for calculating the Z-axis coordinate value of a point on the plane element corresponding to each intersection of a grid set at predetermined intervals on the XY coordinate plane; A means for selecting a value and storing it in correspondence with the XY coordinates of the intersection point, and a means for generating tool path data for controlling the tool in three axes of XYZ based on the stored contents of the storage means. A free-form surface machining information generation system that eliminates tool interference.