JPS6364106A - Processing information generating system for free curved surface evading tool interference - Google Patents

Abstract

PURPOSE:To generate tool path data at a high speed by generating an off-setting polyhedron in accordance with a tool shape from a free curved surface, and when a cross line with a prescribed plane group is overlapped, selecting a necessary cross line and setting a tool path. CONSTITUTION:Three-dimensional free curved surface data from an input device 4 is divided into a picture element for cutting by a free curved surface generating system 1 and the polyhedron off-set from a free curved surface in accordance with the shape of the tool is generated. Based on the polyhedron, a tool path generating system 2 for cutting a free curved surface calculates and stores orthogonal coordinates (X, Z) of the cross line with a plane group in parallel to a Z axis and at an equal interval in a Y axis direction. When the cross line to belong to the plane is overlapped and crossed concerning the X coordinates, based on the X coordinates of an intersection, plural cross lines are divided, the cross line is selected which is the upper-most order and not ovelapped concerning the Z axis and tool path data are generated. Thus, interference and non-interference of the tool are decided and the tool path data to satisfy a necessary processing accuracy are generated at a high speed.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is a three-dimensional free-form surface using an NC machining machine [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, we perform polyhedral approximation consisting of the surface elements for cutting, take out the surface elements one by one, perform sampling on a group of planes parallel to the Z axis, and calculate the intersection line between the surface elements and the plane (X
, Z) coordinates, and if the intersection lines on one sampling plane overlap with respect to the X coordinate and intersect with each other, each intersection line is divided and the upper intersection line is This system is characterized by eliminating tool interference by taking the following steps, improving data generation efficiency and sampling accuracy, and enabling high-speed processing.

(Conventional technology) CAD handles three-dimensional free-form surface data within a computer and generates NG data (tool path data) for automatically machining final products or molds using NC machine tools, etc. from these data. /CAM systems are being put into practical use.

A conventionally known method for generating tool paths is APT (Automatically Prog.
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 includes instructions and definitions regarding workpiece and tool geometry, tool movement relative to the workpiece, machine tool function, tolerances, arithmetic calculations, etc. 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, B6zier has favorable properties for design such as good shape controllability (easy deformation and modification) and easy calculation.
A parametric expression format using a formula or a 9-5 line formula is 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. Not 0 originally CAD/CA
The M system improves efficiency as a whole by transmitting shape information during design to machining, but unlike APT, design is done separately and the tool path for machining is programmed while keeping the required shape in mind. Therefore, no improvement in efficiency can be expected.

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 the other known 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, machining data can be generated in a short time that is practical enough. I can't hope for that at all. In order to perform high-speed processing, the number of data for representing the curved surface is reduced, which results in poor processing accuracy and the ability to satisfy the tolerance of the designed 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 G-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.

For each of the above plane elements, in order to set a tool path on the intersection line between the plane element and a group of planes that are parallel to one of the three axes (Z axis) and spaced at a predetermined interval in the Y axis direction, The apparatus includes means for calculating and storing orthogonal coordinate values (X, Z) of the starting and ending points of each intersection line.

When two lines of intersection belonging to one of the above plane groups overlap and intersect with respect to the A means for selecting a group of intersection lines that do not overlap with each other with respect to the X-axis is provided at a higher level.

When a plurality of intersection lines belonging to one of the plane groups overlap with respect to the X coordinate, means is provided for selecting the one having the maximum Z coordinate among them.

The method further includes means for generating tool path data along the selected intersection line.

[Effect]

This is the tool path generation system most commonly used in 3-axis numerically controlled machine tools that have an orthogonal coordinate system (XYZ axes), and performs tool interference removal processing at high speed in the orthogonal coordinate system.

The process of generating the offset polyhedron and the process of determining the tool path from the offset polyhedron are separated, and the tool path is calculated using the orthogonal coordinate system, but the generation of the offset polyhedron is performed using the B5zier surface, B-5plins surface, Coo
Based on the representation format of geometric surfaces such as ns surfaces.

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.

Further, tool interference removal processing is performed only once for each surface element constituting the offset polyhedron, and redundant calculation processing does not occur, so tool path data can be generated efficiently and at high speed.

The tool path is expressed by the data of a group of line segments obtained by cutting an offset polyhedron with many parallel sampling planes, and the tool interference removal process involves dividing the line segments when they intersect. This is achieved by selecting the top line segments that do not overlap. Therefore, although the processing algorithm is simple and the amount of data handled is small, highly accurate processed data can be obtained.

〔Example〕

<Configuration of the entire G1 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 includes:
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,
A cutting shape (cutting model) 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 l of each side of the approximate polyhedron and the suspended geometric model surface are adjusted so that δ according to the formula falls within the specified intersection. The finishing accuracy preprocessor 21 determines the above sampling width.

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 a cutting process can be realized with a normal 3-axis '411NC 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 (tool movement command position) with respect to the machining surface.

Next, the surface roughness determination preprocessor 22 determines the feed width (feed pitch) 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 tool feed width is halved, the amount of data defining the tool path will double. Therefore, in order to obtain the required finished surface roughness with the minimum tool path data, the tool feed width must be set optimally. The zero surface roughness determination preprocessor 22 calculates the tool feed width that satisfies the given surface roughness. Contains an algorithm for

When using a ball end mill (radius R) as a 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 cutting and finish cutting differ only in tool size, feed width, and presence or absence of finishing allowance, and the data processing algorithm can be considered to be the same.Also, in the rough cutting process, tolerances and surface roughness are not considered. It's fine.

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 in the rough cutting process where the outer 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 with input and output devices through a user interface module 28 . Using input/output devices such as a keyboard, display, and XY profiler, an operator can operate each processor and obtain processing results.

FIG. 3 shows a processing flowchart of the tool path generation system shown in FIG. 2. First, curved surface data is read from a computer file (input PI). 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 designated values and curved surface data, a tool path that avoids tool interference is generated by the rough cutting processor 23 (routine P4). Based on the data generated, the rough cutting tool path, cutting start point, and cutting end point are displayed (display P5
), 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), and then the tolerance class (permissible tolerance) of the registered general tolerance table is specified (operation P9). Next, the preprocessor 21 (
The routine P10) is started, and the finishing accuracy (fineness of division into offset polyhedrons) is determined by comparing the specified tolerance table with the cutting dimensions. Furthermore, the surface roughness value specified in the design drawing is input (operation pH). 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.

Based on the generated tool path data, the tool path for finish cutting is displayed, and the tool interference location is also displayed (displays P14, PI3). If tool interference has occurred, the process returns from judgment P16 to operation P8, partially changes the finishing tool path, and generates 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.

Basic concept of tool path generation process> The tool path generation process consisting of the rough cutting processor 23 and the finish cutting processor 24 basically generates an offset polyhedron from the curved surface data of a geometric model, and then generates a tool from this polyhedron. This is a procedure for generating interference-free tool path data at high speed.

When cutting point A of the free-form surface S with the ball end mill IO as shown in FIG. 4, the point A becomes the point of contact 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 0 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.

In general, an offset vector at a point on a curved surface is a vector that starts from that point and ends at a reference point set in the tool when a 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)=rn (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, considering a free-form surface of parametric representation as shown in Figure 5, the position of the point on the 0-surface W P (X % t, 2)
is given as the period of parameters u, v by xxf, (u, ■) y = 'z (u, v) z = f 3 (u, v) In such a surface, given u, v, , the points on the curved surface and the normal direction can be easily obtained, so by changing u and v, a point sequence (A) is created as shown in Fig. 6, and the corresponding point sequence (A) at the center of the tool is created. O) 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, then X"gl(u,V)"Cl1u'
+C1zu"v+c,,uv"+c, 4v
'+cBu"+c,,uv+cI,v"
+C1, u+C, qV+C, 4)'”gz(u, v)=
C21u3+C2zu” V+Cz3uv! +c, 4
v3+C,%u" +c,, uv+C2yV" +C2
1u+CtqV+cza""gl(u,V)"C31u
'+C3zu" V+c, 3uv" +C3,V3
+C35u” +c34uv+CBV” +c3.
Iu+C3, V+C,.

Consider the offset vector at point P, ~P1° of free-form surface point 10, and its end point Q, -Q,. An offset curved surface can be found as a curved surface passing through . 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 account. For example, when attempting to cut part A as shown in Figure 8 aSb, the necessary part in the vicinity is cut off. This is due to the tool shape. This is due to tool interference. 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 l 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 l.

The point H having the largest value (height) in the Z-axis direction of these intersection points becomes the point on the offset surface where tool interference is avoided. Such an offset curved surface is x of straight line i,
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 the top point of the XY 1000 screen.

As an algorithm for the second step, the "segment height method" in which the Z-axis is calculated with respect to a line segment on the offset plane drawn along the scanning line parallel to the X-axis will be described in detail below.

This algorithm basically provides a solution to the problem of finding the outer envelope of an offset surface.

That is, as shown in FIG. 11, there is a tool path free from interference on the upper surface in the Z-axis direction of the overlapping offset curved surfaces 1.2.

Figure 12 shows the characteristics of the segment height method. In this method, the offset surface is sampled only in one direction, for example along the Y axis, so that the tool path can be generated with high accuracy. . That is, line sampling is performed. It is assumed that sampling is performed at equally spaced positions where the y-coordinate is (yj). Consider the plane y=y= at each position, and find a group of line segments corresponding to the intersection lines when the cross section of the offset polyhedron is taken along this plane.

Is each line segment a plane and each side of a quadrilateral that forms an offset polyhedron? "") can be obtained by sequentially connecting the intersections with Ij.

Next, based on the group of line segments obtained in this way, the 13th
As shown in the figure, by generating a line segment group having the maximum height in the Z-axis direction, a tool path without tool interference can be obtained.

FIG. 14 shows the processing procedure of the segment height method.

Step 1 (Figure 15) 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 1) 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. 15 shows one sheet (batch) of surface elements constituting the 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 (Offset vector F is determined from the normal vector n at each Lmth point. The function F (n) is determined by the tool shape.

Step 3 (17") Divide each quadrilateral on the offset curved surface determined by the end point of the offset vector into two to obtain an offset polyhedron with quadrilaterals as surface elements. Since quadrilaterals do not form a plane, the exact offset No polyhedra are generated.

Step 4 (18-) Prepare a memory array that stores a group of line segments on the offset plane corresponding to each sampling position y in the Y-axis direction. One line segment is represented by the coordinate values of the starting end (XtZii) and the coordinate values of the ending end (X50, zl,).

Note that the sampling interval is equal to or less than the tool feed width Δ calculated by the surface roughness determination preprocessor 22 described above so as to satisfy the surface roughness specified in the drawing.

Step 5 (19゛) Take out one quadrilateral element from the grid on the offset plane,
Find the minimum value 7 sin and maximum value y, , □ of the y coordinate.

Step 6 (2O-) )' sin ~ 7 For yt that falls in the interval of m, t,
Find the intersection points (two) between the plane y-yt and the quadrilateral, and store the coordinates of the intersection (Xz-Zt-) (x
il, zi, ) and repeat this for all quadrilaterals.

Step 7 (21'', 22nd) For each yi, data of the line segment group is used to convert to the highest line segment data in the Z-axis direction.In other words, for yi, as shown in FIG. If a plurality of line segment groups in which Represents a tool path that avoids interference.

Step 8 (23') A tool path can be determined using the coordinate data of the group of line segments in the memory array of FIG. 18 obtained in this way. For example, as shown in Figure 23, while scanning the tool continuously in the X-axis direction at a constant speed, Z-axis control is performed so that the tool height in the Z-axis direction matches each line segment. is moved in steps by pitch Δ. In order to shorten machining time, it is preferable to move the tool along the X axis in a reciprocating manner.

1-Run Algorithm of Segment Height Method Next, a method for speeding up the arithmetic processing required in step 7 of FIG. 14 (FIG. 22) will be explained.

The calculation performed in step 7 is a process of generating the highest line segment group with respect to the Z axis, and is the process that takes the most time. The arithmetic processing is performed on the positional relationships of line segments consisting of the two types shown in FIG. 24a and b and their combinations. Type a is an overlap of two line segments, and type b is a cross of two line segments. In either case, the line segment is redefined to eliminate the dotted line portion.

In type a, if the 0 point Pl, where the line segments P, P, and Q+Qt overlap, is above the line segment QIQt, find the intersection P,' of the straight line x-PIX and the line segment QIQ2, and calculate Z
Line segments higher up with respect to the axis P1 Pz, and Q, P,
' is obtained as a line segment without overlap.

In type b, line segments P, P2 and Q, Q! intersect, so first find the intersection R1. Among the four line segments generated in this way, the one located above with respect to the Z axis is selected to obtain two line segments P, Rz, and RrQx without a cross.

FIG. 25 shows details of the processing procedure in step 7.

In step 6, the end points of the group of line segments representing the offset surface are stored in the memory array in the order determined for each yJ. Each line segment is P isP ta (t = 1.2...
・・・・・・−・・・・・・・−・n, s represents the start end, e represents the end point), the coordinate data of each end point in the memory is P,, = (x, i2 ta ) Pi, = (XiZiJ).

Step 7-1 Exchange xis and Xis so that Xis becomes Xie. In other words, for a line segment whose direction from the start end to the end point is in the negative direction of the X-axis, xi, < xi, so by exchanging only the Since the two coordinates do not change, the height of each line segment, that is, the tool path itself does not change. The purpose of orientation is to limit the tool path to one direction of the X-axis.

Step 7-2 Sort (rearrange) each line segment p, , P, in descending order of Xi, (starting end coordinate). Through this sorting, regardless of the order in which the line segments are sampled, the line segments are rearranged in the order of increasing X coordinates, and tool paths are generated in that order.

Step 7-3 1st and t+1st adjacent line segments PisPi. , P1
．． s Pi*I+a Take out.

■ In the case of X is −X i+I+ s (Figure 26)
If the X coordinates of the end and start ends of two adjacent line segments match, there is no tool interference, so i is incremented by one and two new line segments are taken out.

■ When x, , <xi, 11 (Figure 27) If the X coordinates of the end of the previous line segment and the start of the next line segment are far apart, the predetermined height of zl, 7 Insert the line segments Q, Q, having the values after PilPi*. Due to the insertion, QIQz newly becomes P i, , + l P i *1+ @, and subsequent subscripts are shifted by one.

Furthermore, i is incremented by +1 and the next process is performed.In order to facilitate the insertion and movement of data within the memory, line segment arrangement and data management are actually performed using a pointer structure.

■ When X, 11〉X i + In % (second
(Figure 8) If the end of the previous line segment is located behind the start end of the next line segment with respect to the X-axis, there is overlap between the line segments and tool interference occurs. In this case, the two line segments are divided into a maximum of four sections (1) to (2) as shown in FIG.

(a), xi, ≠ Pi0. In the case of +1, an interval ■ exists.

(b), line segments PisP5* and P i+l+ s P (
When +1+ @ intersects, an intersection point R8 exists, and sections ■ and ■ are formed. If they do not intersect, ■ and ■ become one section.

(C) If ``il #xi*L+ @, the interval ■
exists.

Next, select line segments above the Z-axis in sections ■ and ■. Furthermore, the original line segments Pi, P3. and Pi41+sP i
s1+6 is deleted from the data, and four newly obtained line segments S I'' S v+ are inserted into the interval Xls≠X, , , .

The above step 7-3 is repeated until i-n is reached. However, the value of n (total number) changes during processing.

Through the above processing, it is possible to detect the portion where tool interference occurs and eliminate the interference. Note that in areas where there is no interference, the process simply goes through a loop that goes through the process 1 or 2 in FIG. 25, so very high-speed processing is possible.

In contrast, in the segment height method, as shown in Figure 29, one quadrilateral is extracted from the offset polyhedron, sampled at plane yj, and temporarily stored in the memory area corresponding to y. All line segment data is stored and calculations are performed to remove tool interference based on this data. Since the line segment data is stored in the memory in an appropriate order, it is necessary to perform sorting on the X coordinate as described above. However, since the segment height method handles only the coordinate data at both ends of the line segment, the memory area is also small.Therefore, the segment height method is more efficient in generating tool paths, and can be performed with high precision using a small-capacity data processor. Tool path generation is possible.

FIG. 30 shows a block diagram of the tool path generation system using the segment height method, and each block corresponds to the following program module.

IVIDE Generate an offset polyhedron from a B6zier surface (note that the surface elements are quadrilaterals and not planes).

Generates an offset polyhedron that compensates for discontinuous positions and tangent planes on the parallel U boundary.

LICE Cuts the offset polyhedron with a plane perpendicular to the Y axis to generate a group of line segments.

PVECT Perform calculations to remove tool interference.

RPATH Remove incorrect line segment data caused by calculation errors, etc.

It also removes useless data such as integrating parallel line segments.

〔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 the offset polyhedron. Tool path data can be generated.

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

The tool path is expressed as line segment data (coordinates at both ends of a straight line) obtained by cutting an offset polyhedron for each sampling plane, so there is no deterioration in accuracy due to sampling, and the processor that handles the data can be small ( A very practical automatic addition system is obtained.

Tool interference removal processing is achieved by dividing a line segment when a group of line segments intersects and selecting a higher-order line segment with no overlap. Therefore, although the processing algorithm is simple and the amount of data handled is small, highly accurate processed data can be obtained.

[Brief explanation of the drawing]

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. Figure 4 is a diagram showing the relationship between a free-form surface and an offset curved surface, and Figure 5 is a diagram showing a free-form surface expressed parametrically.
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 offset curved surface, and Fig. 8 is a diagram showing tool interference due to tool shape. 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 line diagram showing the outer surface of an offset curved surface that avoids tool interference, Fig. 12 is a line diagram showing the principle of the segment height method, and Fig. 13 is a line diagram of a group of line segments with tool interference removed. FIG. 14 is a flowchart showing the processing procedure of the segment height method. Fig. 15 is a diagram of the geometric surface corresponding to step 1 of the flowchart in Fig. 14, Fig. 16 is a diagram of the offset vector corresponding to step 2, and Fig. 17 is a diagram of the offset polyhedron corresponding to step 3. , FIG. 18 is a diagram showing the sampling position and data memory arrangement corresponding to step 4, FIG. 19 is a diagram showing the quadrilateral plane elements of the offset polyhedron corresponding to step 5, and FIG. 20 is a diagram corresponding to step 6. Figure 21 is a diagram showing the position of the line segment group corresponding to step 7, Figure 22 is a diagram of the line segment group subjected to tool interference removal processing corresponding to step 7, and Figure 23 is a diagram of the segment sampling performed. is a diagram of the tool path corresponding to step 8. 24a and 24b are diagrams showing overlap and crossing of line segments in the segment height method, FIG. 25 is a flowchart showing details of the processing procedure of step 7 in FIG. 33,
FIGS. 26 to 28 are diagrams showing various B types of positional relationships between two adjacent line segments. FIG. 29 is a diagram showing an outline of the processing procedure of the segment height method, and FIG. 30 is a block diagram of the tool path generation system. In addition, in the symbols used in the drawings, 1. Free-form surface cutting tool path generation system 3------------NC milling machine 4-------1------human power 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; means for calculating and storing orthogonal coordinate values (X, Z) of the starting and ending points of each line of intersection on each of the planes in order to set a tool path on the line of intersection with the group of planes; When two intersection lines belonging to one overlap and intersect with respect to the X coordinate, each intersection line is divided into multiple intersection lines based on the end point and the X coordinate of the intersection point, and A free-form surface machining information generation system that avoids tool interference, comprising means for selecting a group of intersection lines that do not overlap with each other with respect to an axis, and means for generating tool path data along the selected intersection lines.