JP2652848B2 - Machining information generation method for free-form surface avoiding tool interference - Google Patents

Description

The present invention relates to a method for generating machining information (tool path data) for automatically cutting a three-dimensional free-form surface with an NC machining center or the like.

[Summary of the Invention]

When generating tool path data for a numerically controlled machine tool from three-dimensional free-form surface data, a polyhedral approximation consisting of cutting surface elements is performed, and the surface elements are extracted one by one, using a group of planes parallel to the Z axis. Sampling is performed to represent the tool path by the (X, Z) coordinates of the intersection line between the surface element and the plane. If the intersection lines on one sampling plane overlap with respect to the X coordinate and cross each other, The method is characterized in that each intersection is divided and a tool intersection is removed by taking an upper intersection so as not to overlap, thereby improving data generation efficiency and sampling accuracy and enabling high-speed processing.

[Conventional technology]

A CAD / CAM system that handles 3D free-form surface data inside a computer and generates NC data (tool path data) from these data to automatically process the final product or die with an NC machine tool etc. Is being transformed.

APT (Automatically Programmed Tools) is one of the conventionally known methods for generating a tool path. A
The main subject of PT is a general-purpose automatic programming language for multi-axis contour control with a description style similar to English. The language includes instructions and definitions relating to the geometry of the workpiece and the tool, the motion of the tool relative to the workpiece, the capabilities of the machine tool, tolerances, arithmetic calculations, and the like. When a program written in this language is run on a large computer, an NC tape can be output.

On the other hand, when dealing with a curved surface such as a product outer shape in a computer, a Bzier equation or a B-Spline equation, which has properties favorable for design such as good controllability of the shape (easy deformation and correction) and easy calculation, is used. The parametric representation used is often used.

[Problems to be solved by the invention]

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

In the above-mentioned APT, the user instructs (programs) the tool outward path, and as a result, cutting data of the free-form surface is generated, and the tool path is automatically generated from the geometric model generated in the computer. is not. Originally, the CAD / CAM system transmits the shape information at the time of design to the machining, which improves the efficiency as a whole.The design is performed separately like APT, and the tool path for the machining is performed while conscious of the required shape. Efficiency improvement cannot be expected by programming.

On the other hand, a curved surface expressed parametrically is convenient for defining a shape because it does not depend on a coordinate system. However, since the coordinate system of a machine tool for cutting a curved surface is determined, it is not possible to convert the curved surface data generated in the computer into machining data (tool path data) with high accuracy. For this reason, the processing accuracy decreases. In addition, if the cutting is performed directly based on the parametric expression, it is technically difficult to check the interference (collision) between the tool or the tool holder and the finished shape, and there is an inconvenience of cutting a necessary portion.

In other known curved surface representations using polyhedron approximation, sufficient processing accuracy cannot be obtained unless enormous data exceeding the processing capability is handled. Therefore, generation of machining data in a short time enough to be practical cannot be expected at all. If the number of data of the curved surface representation is reduced for high-speed processing, the processing accuracy becomes coarse, and the tolerance of the designed curved surface cannot be satisfied.

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

[Means for solving the problem]

The present invention is a method for generating tool path data for a numerically controlled machine tool of at least three-axis control by processing data representing a three-dimensional free-form surface, comprising: dividing the free-form surface into cutting surface elements; Generating an offset polyhedron that is offset from the free-form surface in accordance with the shape of the surface polyhedron;
In order to set a tool path on a line of intersection with a group of planes parallel to one of the axes (Z-axis) and spaced at predetermined intervals in the Y-axis direction, orthogonal coordinate data of the start and end of each line of intersection ( X, Z), and, when a plurality of intersection lines belonging to one of the plane groups have a portion sharing the X coordinate value, the Z coordinate value of the shared portion Calculating the orthogonal coordinate data (X, Z) at the start and end of each new intersection line having no shared portion by extracting the largest portion, and converting the tool path data along the intersection line group into each plane (Y coordinate).

[Action]

This is a tool path generation system most suitable for a numerically controlled machine tool of three-axis control having an orthogonal coordinate system (XYZ axes), and executes tool interference removal processing at high speed in an orthogonal coordinate system.

The process of generating the offset polyhedron and the process of obtaining the tool path from the offset polyhedron are separated, and the tool path is obtained in the orthogonal coordinate system. It can be based on the expression form of a geometric surface. Therefore, various types of curved surfaces can be processed without depending on the data structure of the curved surface expression. Even if the workpiece is composed of a plurality of curved surfaces, it can be handled in the same manner as a single curved surface.

Also, the tool interference removal processing is performed only once for each of the surface elements constituting the offset polyhedron, and no redundant calculation processing occurs. Therefore, tool path data is efficiently and rapidly generated.

The tool path is represented by data of a group of line segments obtained by cutting the offset polyhedron at a number of parallel sampling planes,
The tool interference removal processing is achieved by dividing a line segment when a group of line segments intersect and selecting a higher-order line segment having no overlap among the line segments. Therefore, high-precision processed data can be obtained despite a simple processing algorithm and a small amount of data to be handled.

〔Example〕

<G ₁ : Overall Configuration of System> FIG. 1 shows the overall configuration of the CAD / CAM system of the embodiment. In FIG. 1, a free-form surface generation processing system 1 includes a CA
In a portion corresponding to D, shape data of a geometric model representing a three-dimensional free-form surface of an object is generated based on an input operation of an operator, and stored in a file. The object is a machined part or a mold.

The created shape data is converted into machining data, that is, data for determining a moving path of the cutting tool in the free-form surface cutting tool path generating system 2. The machining data is dropped on a floppy disk and the NC milling machine 3 (NC
Automatic processing is performed by mounting a floppy disk on a milling machine or a machining center.

The substance of the free-form surface generation processing system 1 and the free-form surface cutting tool path system 2 is a computer, and an input device such as a keyboard and a digitizer and a display device 5 such as a CRT are attached for a user interface.

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

As shown in Figure 2: <G ₂ configuration of the tool path generation system> includes a plurality of program modules is a tool path generation system is activated sequentially or in parallel. Each program module can be considered as a dedicated data processor, and is hereinafter referred to as a processor.

First, the accuracy determination preprocessor 21 and the surface roughness determination preprocessor 22 are activated in the preliminary processing stage. The accuracy determination preprocessor 21 determines the division fineness for dividing the curved surface of the geometric model generated in the CAD stage into a number of quadrilaterals (or triangles) based on the tolerance specified for the target workpiece. decide. By this polyhedral division, a cut shape (cut model) approximated within the tolerance can be generated. By the polyhedral approximation in consideration of the tolerance, it is possible to determine an optimum tool path for executing a cutting process that is not unnecessarily highly accurate and satisfies the design specification.

When the error between the radius of curvature ρ of the geometric surface and the distance from the center to the approximate polyhedron is δ, the equation is The finishing accuracy preprocessor 21 determines the size l of each side of the approximated polyhedron, that is, the sampling width on the geometric model curved surface, so that δ according to 内 is within the designated intersection.

The tool path is set on the generated polyhedron. That is, the tool cuts a curved surface while making a fine linear motion from point to point in space. Such cutting can be realized by a normal three-axis control 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 center of the tool (tool movement command position) with respect to the processing 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. But the tool feed width
By halving, the amount of data defining the tool path is doubled. Therefore, in order to obtain the required finished surface roughness with the minimum tool path data, the tool feed width must be optimally set. The surface roughness determination preprocessor 22 includes an algorithm for calculating a tool feed width that satisfies a given surface roughness.

When a ball end mill (radius R) is used as a cutting tool, the surface roughness determination preprocessor 22 determines that the height H of the uncut portion on the processing surface satisfies the specified surface roughness.
formula Is used to determine the tool feed width △.

The data of the division fineness and the tool feed pitch of the offset polyhedron obtained by the accuracy determination preprocessor 21 and the surface roughness determination preprocessor 22 are passed to a tool path generation processor including a roughing processor 23 and a finishing milling processor 24. Based on these, the curved surface data of the geometric model is sequentially processed, and tool path data is finally generated. It should be noted that the roughing and the finishing are different only in the size of the tool, the feed width, and the presence or absence of the finishing margin, and the data processing algorithm may be considered to be the same. In the roughing process, it is not necessary to consider the tolerance and the surface roughness.

The most important function of these tool path generation processors 23 and 24 is to determine a tool path that avoids tool interference. Tool interference is most likely to occur in a roughing process with a large tool outer diameter. Further, by devising a tool path forming algorithm, these processors 23 and 24 can generate a tool path at high speed.
The generated tool path data is passed 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 finish cutting, and the block material is subjected to milling (milling) cutting.

The tool path generating system shown in FIG. 2 is provided with a parameter cutting processor 25, which can also perform cutting directly based on the original curved surface shape data expressed in parameters. Although the processor 25 does not perform the tool interference check, for a curved surface that can be predicted to cause no interference, parameter cutting can be selected according to the curved surface shape.

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

Each processor or preprocessor of the tool path generation system can transfer data to and from input / output devices through the user interface module 28. Using input / output devices such as a keyboard, a display, and an XY plotter, an operator can operate each processor to obtain a processing result.

FIG. 3 shows a processing flowchart of the tool path generating system of FIG. First, the surface data is read from a computer file (input P1). Next, the surface data is displayed to confirm the data (display P2). Next, the process proceeds to a rough cutting process, in which a rough cutting tool path is generated. In the roughing process, first, a finish allowance and a tool diameter are specified (operation P3). On the basis of these specified values and the curved surface data, a tool path that avoids tool interference is generated by the roughing processor 23 (routine P4). With the data generated by this, the tool path for roughing,
The cutting start point and cutting end point are displayed (display P5). At this time, if there is an unavoidable tool interference part, this is displayed (display P6). When tool interference occurs (judgment P7), the process returns to operation P3 to change the tool diameter, and the tool path is generated again.

When it is determined that there is no tool interference in the determination P7, the process proceeds to the next finish cutting process. In this process, first, a finish tool diameter is specified (operation P8). In addition, specify the tolerance class (tolerance) of the registered general tolerance table (operation P
9). Next, the preprocessor 21 (routine P10) for determining the finishing accuracy is activated, and the finishing accuracy (the fineness of division into offset polyhedrons) is determined by comparing the specified tolerance table with the cutting dimensions. Further, a surface roughness value specified in the design drawing is input (operation P11). By this surface roughness specified value,
The tool feed width is determined by the finish surface roughness determination preprocessor 22 (routine P12).

Next, based on the data of the division fineness and the tool feed width of the polyhedron determined by the allowable tolerance and the designated surface roughness, the finish cutting processor 24 (routine P13) is activated to generate a finish cutting tool path. Based on the generated tool path data, the tool path for finish cutting is displayed and the tool interference location is displayed (displays P14 and P15). If a tool interference has occurred, the process returns from the judgment P16 to the operation P8, where the finish tool path is partially changed, and the tool path is generated again. If the interference is removed by this tool change, the generated tool path data is written to a file, and a series of processing ends.

Tool path generation process consisting of rough processor 23 and the finishing cutting processor 24: <G ₃ basic concept of tool path generation process> generates an offset polyhedron from surface data of the geometric model is basically a tool from the polyhedron This is a procedure for generating tool path data without interference at high speed.

When the point A of the free-form surface S is cut by the ball end mill 10 as shown in FIG. 4, the point A becomes a contact point between the free-form surface and the blade surface of the ball end mill. In this case, the ball end mill 10
A vector (▲) connecting the center O and the point A of the spherical portion is a normal vector at the point A of the free-form surface. This vector is called an offset vector.

Generally, an offset vector at a point on a curved surface is a vector whose start point is a reference point defined in the tool when the tool is brought into contact with the point to cut the point. The vector F is generally a function F (n) of the normal vector n. In case of ball end mill, F
(N) = rn (r is the radius of the spherical portion).

Given an offset vector at every point on a free-form surface, its end point forms one surface. If this curved surface is called an offset curved surface, a desired free-form surface can be machined by moving the tool so that the tool center is clearly on the offset curved surface.

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

For example, consider a free-form surface in a parametric expression as shown in FIG. The position P (x, t, z) of a point on a curved surface is expressed by the following equation: x = f ₁ (u, v) y = f ₂ (u, v) z = f ₃ (u, v) Given as In such a curved surface, when u and v are given, the point and the normal direction on the curved surface can be easily obtained. Therefore, by changing u and v, the point sequence {A} is changed as shown in FIG. The point sequence {O} at the center of the tool can be obtained as the tool path.

As another method, as shown in FIG. 7, there is a method of generating an offset curved surface corresponding to the free curved surface and specifying a point on the offset curved surface parametrically to generate a tool path. For example, if the free-form surface is expressed by the _{following, x = g 1 (u,} v) = c 11 u 3 + c 12 u 2 v + c 13 uv 2 + c 14 v 3 + c 15 u 2 + c 16 uv + c 17 _{^{v 2 + c 18 u + c}} 19 v + c 1A y = g 2 (u, v) = c 21 u 3 + c 22 u 2 v + c 23 uv 2 + c 24 v 3 + c 25 u 2 + c 26 uv + c 27 v 2 + c 28 u + c 29 v + c 2A _{z = g 3 (u, v} ) = c 31 u 3 + c 32 u 2 v + c 33 uv 2 + c 34 v 3 + c 35 u 2 + c 36 uv + c 37 v 2 + c 38 u + c 39 v + a point P ₁ of c _3A free curved point 10 consider the offset vector in to P _10, it is possible to determine the offset curved surface as a curved surface passing through the end point Q ₁ to Q _10. In this offset surface,
By changing the parameters u 'and v', a tool path can be generated.

In the above-described method of generating a tool path, tool interference is not considered. For example, as shown in FIGS. 8a and 8b, when the portion A is cut, a necessary portion in the vicinity is cut off. This is tool interference caused by the tool shape. Alternatively, as shown in FIG. 9, there is a case where it is impossible to avoid the tool interference and cut the portion A unless the angle of the ball end mill is changed. This is tool interference caused by the setting condition of the machining axis.

To find out the tool interference, it is sufficient to calculate the intersection of the ball end mill and the target free-form surface.However, it takes a lot of calculation time to obtain a certain degree of accuracy. The tool path is generated while being checked by humans to prevent the occurrence of a tool path.

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 1 parallel to the Z-axis is considered, and the intersection of this and the offset curved surface is determined. When tool interference occurs, the tool path on the offset curved surface forms a loop as shown in the figure, so that a plurality of intersections H ₁ , H ₂ , and H ₃ are obtained for one straight line l. H ₁ that has the largest value relates the Z-axis direction value of the intersections (height), a point on the offset surface to avoid tool interference. Such an offset curved surface is represented by the x and y coordinates of the straight line 1 and the z coordinate of the intersection.

Specific tool path generation process based on the principles described above: <G ₄ embodiment of the tool path generating process> consists by essentially following steps.

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

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

As an algorithm of the second step, a "segment height method" for calculating the Z-axis for a line segment (segment) on an offset plane drawn along a 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 envelope of an offset surface.

That is, as shown in FIG. 11, there is a tool path without interference on the upper surface in the Z-axis direction among the overlapping offset curved surfaces 1 and 2.

FIG. 12 shows the features of the segment height method. In this method, the offset path 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, sampling is performed with a line. In other words, sampling is performed at each position of the y coordinate of {y _j } at equal intervals. At each position, a plane y = y _j is considered, and a line segment group corresponding to an intersection line when a section of the offset polyhedron is taken along this plane is obtained.

Each of the line group is obtained by connecting the intersections between the sides and the plane y = y _j of rectangles forming the offset polyhedron in order.

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

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

Step 1 (FIG. 15) A normal vector n at a lattice point on the geometric model curved surface is obtained. Each grid point (sample point) is obtained by arranging it in a grid on a curved surface so as to satisfy the required tolerance based on the result (sampling interval 1) of the precision 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 a specified tolerance class.

FIG. 15 shows one sheet (patch) of a surface element constituting the geometric model, which is expressed parametrically by 16 control points. When the patches are subdivided into a lattice shape, division is performed using the result of the precision determination preprocessor 21 so that the final finished shape falls within the tolerance.

Step 2 (FIG. 16) An offset vector F is obtained from the normal vector n at each point. The function F (n) is determined by the tool shape.

Step 3 (FIG. 17) Each square on the offset curved surface determined by the end point of the offset vector is divided into two to obtain an offset polyhedron having the square as a plane element. Since the quadrangle does not form a plane, an offset polyhedron is not accurately generated.

Step 4 To prepare a (FIG. 18) a memory array containing a polyline on the offset surface corresponding to each sampling position y _j of the Y-axis direction. One line segment is represented by coordinate values at the beginning (x _is , z _is ) and at the end (x _ie , z _ie ). The sampling interval is equal to or less than the tool feed width Δ calculated by the surface roughness determination preprocessor 22 to satisfy the surface roughness specified in the drawing.

Step 5 (FIG. 19) One quadrilateral element is extracted from the grid on the offset plane, and the minimum value y _min and the maximum value y _max of the y coordinate are obtained.

Step 6 For y _i enters the section (Figure 20) y _min ~y _max, plane y = y _i and find the intersection (2) between the quadrilateral coordinates of the intersection in the memory array for each y _i (x _is , z _is ) (x _ie , z _ie ). This is repeated for all the quadrilaterals.

Step 7 (FIGS. 21 and 22) Using the data of the line group for each y _i , the data is converted into the top line data in the Z-axis direction. That is, when a plurality of line segment groups overlapping in the Z-axis direction are obtained as shown in FIG. 21 for y _i , the line segments other than the topmost line group are deleted as shown in FIG. Generate group data. The obtained data of the group of line segments represents a tool path in which tool interference has been avoided.

Step 8 (FIG. 23) The tool path can be determined by the coordinate data of the line segments in the memory array of FIG. 18 obtained in this way. For example, as shown in FIG. 23, the Z-axis control is performed so that the tool height in the Z-axis direction matches each line segment while continuously scanning the tool at a constant speed in the x-axis direction. The tool is moved stepwise by a pitch Δ in the Y-axis direction. In order to reduce the processing time, it is preferable that the tool movement on the X axis is performed in a reciprocating manner.

Next, a method for speeding up the necessary arithmetic processing in step 7 (FIG. 22) of FIG. 14 will be described. The calculation performed in step 7 is a process of generating a line segment group at the highest position with respect to the Z axis, and is a process that takes the longest time. Arithmetic processing is
24 The positional relationship between the two types shown in FIGS. Type a is an overlap of two line segments and type b is a cross of two line segments.
In any case, the line segment is redefined to eliminate the dotted line portion.

In type a, the line segments ▲ ▼ and ▲ ▼ overlap. If the point P ₁ is above the line segment ▲ ▼), the intersection P ₁ ′ between the straight line x = P _1x and the line segment ▲ ▼
And the line segment that is higher with respect to the Z axis ▲
▼ and ▲ ▼ are obtained as line segments without overlap.

In the type b, since the line segments ▼ and ▼ intersect, the intersection R1 is _first determined. From the four line segments generated in this way, a line segment above the Z axis is selected, and two line segments without crosses ▲ ▼, ▲
Get ▼.

FIG. 25 shows the details of the processing procedure of step 7. In step 6, the end points of the line segment group representing the offset plane are stored in the memory array in the order determined for each y _j . Each line segment is represented by ▲ ▼ (i = 1, 2,.
Assuming that e represents the end, respectively, the coordinate data of the start end in the memory is as follows: P _is = (x _is , z _is ) P _ie = (x _ie , z _ie ).

Step 7-1: Exchange x _is and x _ie so that x _is <x _ie . In other words, for a line segment in which the direction from the start end to the end is in the negative direction of the X axis, x _ie <x _is , so only the x coordinate of the start end and the end is exchanged, and all the line segments are in the positive direction of the X axis. Orientation to face. Since the z coordinate does not change, the height of each line segment, that is, the tool path itself does not change. The purpose of the orientation is to limit the tool path to one direction of the X axis.

Step 7-2 Sorting (rearranging) in ascending order of each line segment ▲ ▼ (starting point coordinates). By this sorting, no matter what order the line group is sampled, the line group is rearranged in the order of increasing x-coordinate, and the tool path is generated in that order.

Step 7-3: i and i + 1th adjacent line segments ▲ ▼, Take out.

When x _ie = x _{i + 1, s} (FIG. 26) If the x-coordinates of the end and start ends of two adjacent line segments match each other, there is no tool interference. Take out two line segments.

When x _ie <x _{i + 1, s} (FIG. 27) If the x-coordinate between the end of the previous line segment and the start of the subsequent line segment is apart, it has a predetermined height of z _min Line segment ▲
Insert ▼ after ▲ ▼. Insertion changes ▲ ▼ And the subscripts thereafter are shifted one by one. Further, i is incremented by +1 and the following processing is performed. In addition, in order to facilitate insertion and movement of data in the memory, arrangement of line segments and data management are actually performed by a pointer structure.

When x _ie > x _{i + 1, s} (Fig. 28) If the end of the previous line segment is behind the start of the subsequent line segment with respect to the x-axis, there is overlap between the line segments and tool interference occurs. Has occurred. In this case, two line segments are divided into a maximum of four sections I to IV as shown in FIG.

(A), when x _is ≠ P _{i + 1, s} , a section I exists.

(B), line segment ▲ ▼ and Crosses, there is an intersection R _i , and the sections II and III
Can be done. If they do not cross, II and III are one section.

(C), if x _is ≠ x _{i + 1, e} , there is a section IV.

Next, in the sections II and III, a line segment above the Z axis is selected. In addition, the original line segment ▲ ▼ Is deleted from the data, and the four newly obtained line segments S _{I to} S
_{VI is} inserted into the section of x _is ≠ x _{i + 1, e} .

That is, when a plurality of intersections belonging to one of the plane groups y _i have portions (sections II and III) sharing the X coordinate value, the Z coordinate value of the shared portion is the largest. The portion is extracted and the orthogonal coordinate data (X, Z) at each of the start and end of the new intersection line group having no shared portion is calculated. Here, when two intersections intersect, the coordinate value of the intersection R _i of the two intersections that intersect with each other is calculated, and based on the X coordinate values of the start, end, and intersection of each intersection, It is divided into a plurality of partial intersecting lines composed of the above-mentioned shared portion (sections II and III) and non-shared portions (sections I and IV) other than the shared portion. Then, a new intersection line group (line segments S _{I to} S _IV ) composed of the upper portion of the shared portion with respect to the Z axis and the non-shared portion. Is selected to generate the orthogonal coordinate data (X, Z) at the start and end of this intersection line group. If the two intersection lines do not intersect, the interval II, II
Since I is one section, as described above with reference to FIG. 24 (a), a higher-order part in the Z-axis direction among the shared parts is selected.

Step 7-3 is repeated until i = n.
However, the value of n (total number) changes during processing.

By the above processing, the part where the tool interference occurs can be detected and the interference can be eliminated. If there is no interference,
Very high-speed processing is possible because it simply loops through the processing of or of FIG.

As described above, in the segment height method, as shown in FIG. 29, one quadrilateral is extracted from the offset polyhedron, sampled on a plane y _j , and temporarily stored in a memory area corresponding to y _j. All the line segment data are stored, and an operation for removing tool interference is performed based on this data. Since the line segment data is stored in the memory in an appropriate order, as described above, x
You need to sort the coordinates. However, since only the coordinate data at both ends of the line segment is handled in the segment height method, the memory area may be small. Therefore, the segment height method is more efficient in generating a tool path, and a high-precision tool path can be generated with a small-capacity data processor.

FIG. 30 is a block diagram showing a tool path generation system based on the segment height method. Each block corresponds to the following program module.

Generates an offset polyhedron from a DIVIDE Bzier surface (the surface elements are quadrilaterals and not planes).

Generate an offset polyhedron that compensates for discontinuities in the position and tangent plane at the EDGE boundary.

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

DPVECT Performs operation to remove tool interference.

CRPATH Eliminates incorrect line segment data caused by calculation errors. In addition, unnecessary data such as integration of parallel connected segments is removed.

〔The invention's effect〕

As described above, the present invention obtains a tool path by an intersection line between a plane element and a plane for each plane element of an offset polyhedron, and when a plurality of intersection lines overlap on the same plane, a maximum intersection line of the Z coordinate is determined. Since tool interference removal is performed, the start and end points of the intersection
Since the tool path can be defined by the coordinates of the points, the calculation of the tool path data is extremely simplified, and all of the intersection lines generated as the tool path for a certain offset plane element and all plane elements of the offset polyhedron are determined. There is no need to check the relationship, and the process of selecting and storing the higher-order intersection line of the Z-axis only needs to be performed once for each intersection line of the one-plane element, and there is no redundant calculation process for the tool interference removal process. Therefore, the tool path generation efficiency is high and high-speed processing is possible.

Also, a plurality of intersection lines on the same plane overlap with respect to the X axis,
In addition, in the case of intersection, if the tool segment is removed by dividing the line segment at the intersection and selecting a higher-order line segment having no overlap, the processing algorithm is simplified, and the amount of data to be handled is reduced. However, since highly accurate tool path data can be obtained, the efficiency of tool path generation is high, and high-speed processing is possible.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a tool path generating system according to the present invention.
FIG. 2 is a block diagram of a tool path generation system, and FIG. 3 is a flowchart of a data processing procedure of the tool path generation system. FIG. 4 is a diagram illustrating a relationship between a free-form surface and an offset surface, FIG. 5 is a diagram illustrating a free-form surface in a parametric expression, FIG. 6 is a diagram illustrating one method of generating a tool path from the free-form surface, FIG. 7 is a diagram showing one method of generating a tool path from an offset curved surface, FIG. 8 is a sectional view showing tool interference caused by a tool shape, and FIG. 9 is a diagram showing tool interference caused by a setting condition of a machining axis. FIG. 10 is a sectional view showing a tool interference test method. FIG. 11 is a diagram showing the envelope surface of the offset curved surface avoiding tool interference, FIG. 12 is a diagram showing the principle of the segment height method, FIG. 13 is a diagram of a group of line segments from which tool interference has been removed, FIG. 14 is a flowchart showing a processing procedure of the segment height method. 15 is a diagram of a geometric surface corresponding to step 1 of the flowchart of FIG. 14, FIG. 16 is a diagram of an offset vector corresponding to step 2, and FIG. 17 is a diagram of an offset polyhedron corresponding to step 3. FIG. 18 is a diagram showing a sampling position and a data memory array corresponding to step 4, and FIG.
FIG. 19 is a diagram showing a quadrilateral face element of the offset polyhedron corresponding to step 5, FIG. 20 is a diagram of segment sampling corresponding to step 6, and FIG. 21 is a diagram showing a position of a group of line segments corresponding to step 7. FIG. 22 is a diagram of a group of line segments subjected to the tool interference removal processing corresponding to step 7, and FIG. 23 is a diagram of a tool path corresponding to step 8. 24a and 24b are diagrams showing overlap and cross of line segments in the segment height method, FIG. 25 is a flowchart showing details of the processing procedure of step 7 in FIG. 14, FIGS. 26 to 28 FIG. 4 is a diagram showing various aspects of the positional relationship between two adjacent line segments. FIG. 29 is a diagram showing an outline of a processing procedure of the segment height method, and FIG. 30 is a block diagram of a tool path generating system. In addition, in the code | symbol used for drawing, 1 ... Free-form surface generation processing system 2 ... Tool path generation system for free-form surface cutting 3 ... NC milling machine 4 ... Input device 5 ... Display 21 ... Precision determination preprocessor 22 … Surface roughness determination preprocessor 23… Roughing processor 24… Finishing processor.

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Claims (2)

(57) [Claims] 1. A method of processing data representing a three-dimensional free-form surface to generate tool path data for at least a three-axis control numerically controlled machine tool, comprising: dividing the free-form surface into cutting surface elements; Generating an offset polyhedron offset from the free-form surface in accordance with the shape of the tool; and for each surface element constituting the offset polyhedron, a surface element and a Y-axis parallel to one of three axes (Z-axis). In order to set the tool path on the line of intersection with the plane group at a predetermined interval in the direction, the orthogonal coordinate data (X,
Calculating and storing Z), and when a plurality of intersections belonging to one of the plane groups have a portion sharing an X coordinate value, Z of the shared portion
Calculating the orthogonal coordinate data (X, Z) of the start and end of each new intersection line group having no shared portion by extracting the portion having the largest coordinate value; and calculating the tool path data along the intersection line group. Each plane (Y coordinate)
Generating machining information of a free-form surface from which tool interference has been eliminated, comprising: 2. A method according to claim 1, wherein the plurality of intersections belonging to one of the plane groups are X
In the case where there is a portion sharing the coordinate values, the portion having the largest Z coordinate value among the shared portions is extracted, and the orthogonal coordinate data at the start and end of each new intersection line group having no shared portion ( X, Z): calculating the coordinate value of the intersection of two intersections that intersect each other; and the shared part based on the X-coordinate values of the start and end of each intersection and the intersection. And dividing into a plurality of partial intersections consisting of non-shared portions other than the shared portion; and selecting a new intersection line group consisting of the upper portion of the shared portion with respect to the Z axis and the non-shared portion. Generating the orthogonal coordinate data (X, Z) of each of the start end and the end of the intersection line group.