JP3010002B2 - Tool path calculation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calculating a tool path in a CAD (Computer Aided Design) / CAM (Computer Aided Production) system or the like for forming a die to obtain a three-dimensional shape. .

[0002]

2. Description of the Related Art With the recent development of computers, CA
NC processing by a combination of an apparatus for creating processing data such as D / CAM and an NC processing machine has been generally performed. Among them, the processing of a complex and high-value-added three-dimensional product depends on the performance of an NC data creation device such as a CAD / CAM system. Among them, in particular, the technique of calculating a tool path that defines the movement of a tool used for machining is becoming more important as the performance of the technique determines the superiority of a three-dimensional CAD / CAM system or an automatic programming device as a whole.

[0003] Here, the tool path is a tool center point (FIG. 18) which a tool has in its own shape depending on its shape.
(See reference numeral 1). Even if the shapes to be formed (required shapes) are the same, if the shapes of the tools are different, the tool center points are different and the tool paths are different. For example,
When a ball end mill is used, a line 2 as shown in FIG. 19 becomes a tool center locus line. When a flat end mill is used, a line 2 as shown in FIG. 20 becomes a tool center locus line.

In calculating a tool path in such a CAD / CAM system, tool interference (a phenomenon in which a tool cuts too much into a shape part) and a path drop (a tool malfunctions in the middle of a tool path) for various three-dimensional shapes. It is very important that the tool does not fall down significantly below the material).

[0005]

However, in the conventional tool path calculation method, as described below, there are problems of tool interference and path drop, high speed of calculation, fidelity to required shape, tool shape and required shape. There are various problems in terms of flexibility and the like.

Next, a conventional tool path calculation method and its problems will be briefly described. FIG. 21 is a conceptual diagram showing the concept of the positive offset method two-dimensionally. In this positive offset method, a curved surface model of a shape to be manufactured is replaced with a small simple figure within an allowable error range or a curved surface model is replaced with a group of points, and a tool center locus is obtained by offsetting a tool shape as it is. It is. However, in this positive offset method, there is a part where tool interference occurs even if the tool center is moved along the offset plane depending on the shape, and a small gap may be formed between the offset planes, which causes a problem of dropping a path. is there.

FIG. 22 shows the concept of the inverse offset method as follows.
It is a conceptual diagram shown dimensionally. The reverse offset method is a method utilizing the idea that the tool shape is reversed and the envelope surface of the tool shape when the tool center of the reversing tool is moved along the surface of the required shape becomes the desired tool center locus surface. . However, this reverse offset method has the advantage that there is no tool interference or path drop.However, when actually calculating with a computer, a fixed point cloud is generated on the surface of the inverted tool shape, and a fixed pitch on the required shape is obtained. Since it is necessary to find a point that becomes an envelope for each point, there is a problem that the amount of calculation is enormous and a lot of calculation time is required. If the point group pitch is roughly set by rough machining, interpolation must be performed between the point groups depending on the tool shape. There is a problem that it does not become a locus line.

There is also known an analytical method in which a tool shape and a required shape are represented by a curved surface formula, and the contact points thereof are mathematically obtained to obtain a tool center locus contact line. However, in this method, the calculation formula and the calculation method are extremely complicated to calculate the tool center position analytically corresponding to any shape, and the calculation time is extremely long. If the formula is incomplete due to a calculation error or the like, an accurate tool center trajectory line cannot be obtained, causing a problem that tool interference or a path drop occurs.

Further, as conceptually shown in FIG. 23, the required shape is replaced with a polygonal line group that sufficiently approximates the shape within the required accuracy, and the tool shape is moved downward from the point on the guide curve to the tool axis. There is also known a contact calculation method in which a position where a model and a tool shape first contact each other is a solution at that point. However, in this contact calculation method, there is a problem that a tool center locus line faithful to a required shape cannot be obtained because a curve is approximated.

The present invention has been made in view of such problems of the conventional tool path calculating method, and it is possible to obtain a tool center trajectory line which is faithful to a shape to be machined without dropping a path or tool interference. It can output NC data in a format suitable for the shape to be machined (relevance of the tool path) and can output NC data in a format suitable for the shape to be processed (appropriateness of NC data). In addition, it is possible to check for interference with the tool holder and the spindle head of the machine (flexibility to the tool shape), and it can be applied to various machining methods for all three-dimensional shapes (flexibility to the machining shape). It is an object of the present invention to provide a tool path calculation method capable of greatly reducing the calculation time for obtaining a trajectory (high-speed calculation).

[0011]

In the method of calculating a tool path for three-dimensional machining according to the present invention, (a) a required three-dimensional shape to be machined is defined by a plane (a plane or a curved surface) parallel to the tool advancing direction. A required shape cutting line group at the time of cutting at a predetermined cutting pitch is obtained, and a tool shape used for machining (the tool shape here is a shape of a tool used for machining, a tool used for machining, and the tool And the shape that requires interference checking, including the holder and the spindle head of the machine, etc. The same shall apply hereinafter.) On a plane (plane or curved surface) parallel to the tool advancing direction at every predetermined cutting pitch. (B) associating the required shape cutting line group and the tool shape cutting line group obtained in this step with each cutting pitch, and To obtain a group of "cut lines" (C) From the “pair of cutting lines” in the “pair of cutting lines” group obtained in this step, a tool section center locus line for each of the predetermined cutting pitches is obtained, thereby obtaining a tool section center. A step of obtaining a group of trajectory lines; and (d) converting a group of trajectory lines of the tool cross-section at one tool feed pitch obtained in this step into a plane (plane or curved surface) parallel to the tool advancing direction and perpendicular to the tool pitch feed direction. Projecting a projection line group at the one tool feed pitch by projecting the above, and (e) selecting a tool advancing direction and a tool pitch from the projection line group at the one tool feed pitch obtained in the step. Taking out the most departed part from the required shape in a direction perpendicular to both of the feed directions and connecting these parts to obtain a tool center trajectory line at the tool feed pitch. It is a symptom.

In the present invention, the steps (d) and (e) are desirably performed for each tool feed pitch, and the steps are preferably repeated for all the tool feed pitches. The steps (a), (b) and (c) may be performed for each tool feed pitch, or may be performed for all tool feed pitches.

In the step (c), when the tool section center locus line for each of the predetermined cutting pitches is obtained from each of the pair of cutting lines in the group of cutting lines, the cutting line To obtain a tool section center locus line by directly offsetting (interference line projection method), and to obtain a section center at a point level where the cutting line of the required shape and the tool section shape are further cut along a plane group perpendicular to the tool advancing direction A method (interference point projection method) is also possible, and a method of obtaining a tool section center locus line by combining both methods is also possible.

[0014]

When a three-dimensional shape is machined using an NC cutting machine such as a machining center, there are various methods of moving a tool, such as scanning line machining, contour line machining, and along surface machining. The tool path in these machining methods is basically a plane (plane or curved surface) consisting of the center axis of the tool and its traveling direction.
It can be treated as a set of upper curves. Therefore,
The present inventor has found that the path calculation for finding the trajectory of the tool center is more efficient and more accurate than for finding the tool center point and interpolating them. Focusing on this idea, a path calculation method (interference line projection method or interference point projection method, in which a tool center trajectory line group is obtained by projecting an interference line between a tool shape and a required shape. In such a case, both of them may be included), and the tool path calculation method of the present invention has been proposed.

In the inverse offset method, which is a conventional typical tool path calculation method, it is necessary to perform calculations based on the concept of the above-described inverse offset method for each point of a constant pitch. In the method, since the calculation applying the concept of the interference ray projection method is performed for each line of a fixed pitch, it is not a point-level calculation but a line-level calculation, greatly reducing the number of calculation steps and greatly reducing the calculation time. It becomes possible.

The tool path calculation method according to the interference line projection method of the present invention can be applied to various processing methods such as scanning line processing, contour line processing, and along-plane processing.
It is possible to calculate an accurate path with necessary accuracy irrespective of a tool shape, a shape to be cut, and the like.

Further, according to the present invention, it is possible to calculate a tool path which can faithfully realize a shape to be machined without tool interference or path drop. That is, in the contact calculation method, which is one of the conventional tool path calculation methods, it is necessary to replace the broken line group that approximates the required shape, so that an error occurs and a tool path cannot be calculated faithfully to the required shape. However, in the tool path calculation method of the present invention, since the calculation is performed using the required shape as it is, it is possible to calculate the tool path with high accuracy. Further, according to the present invention, NC data in a format suitable for the shape to be processed can be obtained.

Further, in the present invention, not only the tool shape but also the tool shape cutting line for obtaining the tool center locus line is used.
Since it is possible to use cutting lines of shapes that require interference checking, including tool holders and machine spindle heads, interference checking between specially shaped tools and required shapes, which was not possible with conventional tool path calculation methods, It is possible to check for interference with tool holders other than tools and the spindle head of the machine.

[0019]

Next, a method of calculating a tool path according to an embodiment of the present invention will be conceptually described with reference to the drawings.

(1) In the tool path calculation method of the present embodiment,
First, the required shape to be manufactured (FIG. 1) is set on a surface parallel to the tool advancing direction (this surface may be flat or curved).
Cutting is performed at a predetermined cutting pitch (FIG. 2), and a cutting line group which is a set of these cutting lines 3 is taken out (FIG. 3). In this embodiment, the cutting pitch is, for example, 3 in the rough finishing.
The pitch is ５5 mm, the pitch is 1 to 2 mm for the medium finish, and the pitch is 0.1 to 0.2 mm for the final finish.

(2) Next, the tool shape to be used (FIG. 4. Note that the tool shape includes not only the shape of the tool, but also the shape of the tool holder and the spindle head of the machine that need to be checked for interference. Are cut at a predetermined cutting pitch on a plane parallel to the tool advancing direction (this plane may be a flat surface or a curved surface, but it is a flat surface here) (FIG. 5). A cutting line group, which is a set of four, is extracted (FIG. 6).

(3) A group of cutting lines obtained by cutting the required shape and a group of cutting lines obtained by cutting the tool shape are made to correspond to each cutting pitch. A group of “pair of cutting lines” is obtained as a set within the range of one pass (tool feed pitch) of the corresponding “pair of cutting lines” (FIG. 7).

(4) Then, a set of cutting lines (a pair of cutting lines) is taken out of the “pair of cutting lines” group (FIG. 8).

(5) With respect to the set of cut-out lines taken out, a tool section center locus line 5 offset by a tool radius from the cut line of the required shape is obtained (FIG. 9).

(6) Tool section center locus line 5 as shown in FIG. 9 for each of "a pair of cutting lines" within the range of one pass (one tool feed pitch) shown in FIG.
(FIG. 10A), and a group of tool section center locus lines corresponding to one pass is extracted (FIG. 10B).

(7) A plane parallel to the tool advancing direction and perpendicular to the tool pitch feed direction (XZ plane in FIG. 10B) for the group of tool section center locus lines shown in FIG. 10B.
A projection line group, which is a set of projection lines 6 projected as if light were applied from the lateral direction, is obtained above (FIG. 11).

(8) From the projection line group, X in FIG.
A portion having the highest Z value on the Z plane (that is, a portion farthest from the required shape in a direction perpendicular to both the tool advancing direction and the tool pitch feed direction) is extracted, and a line 7 connecting them is obtained (FIG. 12). This line 7 becomes the tool center locus line in this one pass (one tool feed pitch).

(9) The above processes (3) to (8) are performed
Perform for all other passes (tool feed pitch).

The tool path calculation method according to the present embodiment as described above is executed by being incorporated in a conventional CAD / CAM system. Here, a specific procedure of execution of the present embodiment will be described based on the flowcharts of FIGS.

First, the entire tool path calculation method according to the present embodiment will be described with reference to FIG. In this embodiment, first, conditions such as a required shape, a tool shape, and a tool feed pitch are defined (step S1). Then, within each of the tool feed pitches, a cutting line is created for each of the required shape and the tool shape at a predetermined pitch on a plane parallel to the tool advancing direction (step S2). Next, from the cutting line of the required shape and the cutting line of the tool shape respectively corresponding to each cutting pitch, a tool section center locus line in which the tool center point is offset from the required shape cutting line is obtained (step S3).
Offset processing). The tool section center locus line group determined in step S3 is projected on a plane (the XZ plane) parallel to the tool advancing direction and perpendicular to the tool pitch feed direction, and the highest portion, that is, the portion having the largest Z value is determined. Take out (interference calculation processing of step S4). This step S4
By connecting the parts extracted in the above, a tool center locus line at the tool feed pitch is obtained (step S5). Next, the process proceeds to step S6, in which it is determined whether or not the processes from steps S2 to S5 have been performed for all the tool feed pitches. If NO, the process returns to step S2, and the same process is repeated. To end.

Next, the processing operation of the condition definition in step S1 of FIG. 13 will be described with reference to FIG. First, a solid shape is instructed (step S11), a tool such as an end mill diameter and a remaining margin is designated (step S12), a machining area which is a range to be machined is designated (step S13), a cutting direction and a cutting pitch. Is specified (step S14), and a division pitch (cutting pitch) indicating how much the tool is to be divided (cut) is specified as the calculation accuracy (step S15), and all of these processes are specified. It repeats until it does (step S16). Thereby, the condition is defined.

Next, the operation of the cross-section line forming process in step S2 in FIG. 13 will be described with reference to FIG. First, the shape (plane, etc.) of the tool slice cross section is defined (step S21), and the intersection between the curved surface of the required shape and the cross section in the tool advancing direction is obtained for each predetermined cutting pitch (step S2).
2) This is performed for all cutting pitches within one tool feed pitch (step S23). As a result, a sectional line having the required shape is created.

Next, the operation of the offset processing of the required shape section line in step S3 in FIG. 13 will be described with reference to FIG. First, each intersection line in the intersection line group obtained in steps S22 and S23 is offset-processed one by one (step S3).
1). If the offset lines obtained in the offset processing in step S31 are far apart, interpolation is performed for connection (step S32: connection processing between curves). In addition, when the gap between the offset lines obtained in the offset processing in step S31 interferes with another offset line, the interference is removed (step S33: self-interference removal processing). The above operation is repeated until all the intersection lines are processed (step S34). As described above, the offset processing of the required shape section line is performed.

Next, the operation of the curve group interference calculation processing of FIG. 13 will be described with reference to FIG. First, step S
The one corresponding to the first cutting pitch in the group of offset lines obtained in step 34 is extracted and used as an original section (step S41: definition of original section). Next, an offset line corresponding to the next cutting pitch is taken out and set as the next section (step S42; definition of the next section). The outer shape is created by removing the interference between the original section and the next section, that is, the data of the portion where the Z value is not higher in the XZ plane between the original section and the next section is removed. Only the portion is taken out (step S43, self-interference processing between cross sections). The cross section from which interference has been removed in this way is defined as the original cross section (step S44). The above operation is repeated for the cross sections of all the cutting pitches in the one pass (step S45). As described above, the line having the largest Z value, that is, the tool center locus line is obtained from the offset line group for each predetermined cutting pitch in the one pass.

A series of operations described above with reference to FIGS. 14 to 17 are operations for obtaining a tool center trajectory line for one pass (one tool feed pitch). This series of operations is performed for all the paths. Repeat (Step S6 in FIG. 13). As a result, the tool center trajectory line can be obtained for all paths (all tool feed pitches).

[0036]

According to the interference line projection method of the present invention, when the tool center trajectory line is determined, calculation is performed for each line of a constant pitch by applying the concept of the interference line projection method. Instead of the point-level calculation as described above, the calculation is performed at the line level, so that the number of calculation steps can be significantly reduced, and the calculation time can be significantly reduced.

The tool path calculation method according to the interference line projection method of the present invention can be applied to various processing methods such as scanning line processing, contour line processing, and along-plane processing.
It is possible to calculate an accurate path with necessary accuracy irrespective of the tool shape and the shape to be cut.

Further, according to the present invention, it is possible to calculate a tool path which can faithfully realize a shape to be machined without tool interference or path drop. That is, in the contact calculation method, which is one of the conventional tool path calculation methods, it is necessary to replace the broken line group that approximates the required shape, so that an error occurs and a tool path cannot be calculated faithfully to the required shape. However, in the tool path calculation method of the present invention, since the calculation is performed using the required shape as it is, it is possible to calculate the tool path with high accuracy. Further, NC data in a format suitable for the shape to be processed can be obtained.

In the present invention, not only the tool shape but also a cutting line of a shape requiring interference check including a tool holder and a machine spindle head is used as the tool shape cutting line for obtaining the tool center locus line. Because it can be used, it is possible to check the interference between the specially shaped tool and the required shape, and the interference between the tool holder other than the tool and the spindle head of the machine and the required shape, which was not possible with the conventional method Becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a required shape to be manufactured.

FIG. 2 is a view for explaining an operation of cutting the required shape of FIG. 1 at a predetermined cutting pitch on a plane parallel to a tool advancing direction.

FIG. 3 is a diagram for explaining an operation of extracting a cutting line having a required shape in FIG. 2;

FIG. 4 is a perspective view showing the shape of a tool used for machining.

FIG. 5 is a view for explaining an operation of cutting the tool shape of FIG. 4 at a predetermined cutting pitch on a plane parallel to the tool advancing direction.

FIG. 6 is a view for explaining an operation of extracting a cutting line of the tool shape of FIG. 5;

7 is a diagram for explaining an operation of associating the cutting line of the required shape in FIG. 2 with the cutting line of the tool shape in FIG. 5 for each cutting pitch.

8 is a diagram for explaining an operation of extracting a pair of a cutting line having a required shape and a cutting line having a tool shape, which are associated with each other in FIG. 7;

FIG. 9 is a diagram for explaining an operation for obtaining a tool section center locus line of the section shape taken out in FIG. 8;

FIG. 10 is a diagram for explaining an operation of extracting a group of tool section center trajectory lines by repeating the operation of FIG. 9;

FIG. 11 shows a group of tool section center locus lines obtained in FIG.
FIG. 9 is a diagram for explaining an operation for obtaining a projection line group projected on an XZ plane of 0.

FIG. 12 is a diagram for explaining an operation of obtaining a line connecting a portion having the largest height from the projection line group of FIG. 11;

FIG. 13 is a flowchart illustrating an operation when the tool path calculation method based on the interference ray projection method of the present invention is executed by a computer, and is a flowchart illustrating an entire tool path calculation operation;

14 is a flowchart for explaining the operation of the condition definition in step S1 of FIG.

FIG. 15 is a flowchart for explaining a cross-section line creation processing operation of the shape in step S2 of FIG. 13;

FIG. 16 is a flowchart for explaining the offset operation of the shape section line in step S3 of FIG. 13;

FIG. 17 is a flowchart for explaining an interference calculation processing operation using a projection line group in step S4 in FIG. 13;

FIG. 18 is a diagram for explaining a tool center point.

FIG. 19 is a diagram showing a tool center locus line when a ball end mill is used.

FIG. 20 is a diagram showing tool center locus lines when a flat end mill is used.

FIG. 21 is a conceptual diagram for explaining a conventional positive offset method.

FIG. 22 is a conceptual diagram for explaining a conventional inverse offset method.

FIG. 23 is a conceptual diagram for explaining a conventional contact calculation method.

[Description of Signs] 1 Tool center point 2 Tool center locus line 3 Cutting line of required shape 4 Cutting line of tool shape 5 Tool cross section center locus line 6 Projection line 7 Tool center locus line

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshifumi Katakura 1-5-15 Hikino, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Computer Engineering Co., Ltd. (56) References JP-A-3-280107 (JP, A) JP-A-6-28020 (JP, A) JP-A-4-273503 (JP, A) JP-A-4-111002 (JP, A) JP-A-2-178709 (JP, A) JP-A-2-23404 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G05B 19/4093-19/4097

Claims (1)

(57) [Claims] 1. A method for calculating a tool path for three-dimensional machining, comprising: (a) cutting a required shape when a required three-dimensional shape to be machined is cut at a predetermined cutting pitch on a plane parallel to a tool advancing direction; In addition to obtaining the line group, the shape of the tool used for machining or the shape that requires interference checking including the tool used for machining and its tool holder and the spindle head of the machine (hereinafter, these are collectively referred to as “tool shape”) Obtaining a group of tool shape cutting lines when the tool is cut at a predetermined cutting pitch in a plane (plane or curved surface) parallel to the tool advancing direction; and (b) a required shape obtained in the step (a). A step of associating a cutting line group with a tool shape cutting line group for each of the cutting pitches to obtain a corresponding “pair of cutting lines” group; and (c) a step obtained by the step (b). Each "pair" in the "pair of cutting lines" group From the cutting line ”, a tool section center locus line group is obtained for each of the predetermined cutting pitches, thereby obtaining a tool section center locus line group; and (d) one of the one obtained in the above step (c). The tool section center trajectory line group at the tool feed pitch is defined as a plane (plane or curved surface) parallel to the tool advancing direction and perpendicular to the tool pitch feed direction.
(E) projecting a projection line group at the one tool feed pitch by projecting the projected line group at the one tool feed pitch from the projection line group at the one tool feed pitch obtained at the step (d). Obtaining the tool center trajectory line at the tool feed pitch by taking out the most deviated part from the required shape in a direction perpendicular to both the direction and the tool pitch feed direction and connecting these parts. Tool path calculation method to be used.