JP2830026B2 - Free-form surface machining data creation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Field of application in industry B Outline of the invention C Conventional technology (Figs. 7 and 8) D Problems to be solved by the invention (Figs. 7 to 10) E Means for solving problems (FIGS. 1 to 6) F function (FIGS. 1 to 6) G embodiment (FIGS. 1 to 6) Effect of the invention A Industrial application field The present invention relates to free-form surface machining data. Regarding the creation method, for example, CAD / CAM (computer aided design / computer aided ma
The present invention is suitably applied to the case where a product having an outer shape having the free-form surface is cut using data representing the free-form surface generated in the manufacturing process.

B SUMMARY OF THE INVENTION The present invention relates to a free-form surface machining data creation method for generating free-form surface machining data representing a moving path of an upper end of a cutting edge of a tool formed of an end mill. By generating the free-form surface processing data representing the moving path, the movement limit of the end mill with respect to the patch representing the free-form surface can be detected.

C Prior Art For example, when designing the shape of an object having a free-form surface using a CAD method (geometric modeling), a designer generally uses a plurality of points in a three-dimensional space through which the surface passes (this is called a node). Is specified, and a computer calculates a boundary curve network connecting the plurality of specified nodes using a desired vector function, thereby forming a curved surface represented by a so-called wire frame.

Thus, a large number of framework spaces surrounded by the boundary curves can be formed (such a process is called a framework process).

The boundary curve network formed by such framework processing is
It itself represents the rough external shape that the designer intends to design, and if it is possible to interpolate a curved surface that can be expressed by a parametric vector function using the boundary curves surrounding each framework space, the designer as a whole will Can generate a free-form surface (which cannot be defined by a quadratic function).

Here, the curved surface formed in each frame space forms a basic element constituting the entire curved surface, and this is called a patch.

By the way, in order to have a more natural outer shape as a whole of the generated free-form surface, a patch that satisfies the condition of continuation of the tangent plane at the boundary curve is set in a frame space adjacent to the boundary curve. There has been proposed a free-form surface creation method in which control edge vectors around a boundary curve are reset (Japanese Patent Application No. 60-277488).

This free-form surface creation method uses, for example, two patches as shown in FIG. Nodes are given by the framework processing to connect Based on adjacent patches Control edge vector that satisfies the condition of tangent plane continuation on the boundary curve COM12 of Are set, and the internal control points are set by these control edge vectors. The principle is to set again.

Patching such a technique Applying to other boundary curves surrounding Are smoothly connected to adjacent patches under the condition of tangential plane continuity.

In this specification, the tangent plane means a plane formed by tangent vectors in the u and v directions at each point of the boundary curve. For example, for each point on the boundary curve COM12 in FIG. When the tangent planes are the same, the condition of continuation of the tangent plane holds.

Here, the condition of the continuation of the tangent plane with respect to the point (0, v) on the boundary curve COM12 is determined as shown in FIG. Ie patch For the direction transverse to the boundary surface COM12 (ie, u
Direction) tangent vector And the tangent vector in the direction along the boundary curve COM12 (ie, v direction) Normal vector Is Represented by a patch For the tangent vector in the direction transverse to the boundary curve COM12 Tangent vector in the direction along the boundary curve COM12 Normal vector Is It is represented by

Under such conditions, the tangent vector Must lie on the same plane, so that the normal vector In the same direction.

To achieve this, the following equation So that the internal control points as well as Should be set. Where λ (v), μ (v), ν
(V) is a scalar quantity.

Also patch Next formula Is a parametric vector function consisting of a cubic Bezier equation Is expressed using Note that u and v are parameters in the u and v directions, respectively, and E and F are shift operators.

Problems to be solved by the invention D Patches generated in this way For example, when cutting a product with the external shape represented by the following using a 3-axis control type NC milling machine as a CAD / CAM system, Like the patch that is the cutting target Offset vector representing the position data representing the surface of Offset surface consisting of just moved surface And generate the offset surface It is considered that the movement of the tool of the NC milling machine should be controlled based on the position data representing the surface of the machine (Japanese Patent Application No. 61-2085).
No. 51).

Where the offset vector Is a patch as shown in FIG. Normal vector Is a function that is determined by the shape of the tool edge. A vector whose origin is the top point and whose end point is the reference point defined in the tool, and the reference point of the tool is an offset surface When moving up, the cutting edge is the The function is predetermined so that it can move along the surface of.

Actually, a three-axis control type NC milling machine is used which has a configuration in which the cutting edge of the tool is directed downward (in the Z-axis direction). For example, as a tool suitable for cutting a shape of a free-form surface as described above, a cutting edge generally has a predetermined radius R _BM (=
Hemispherical ball end mill BM having an axial radius) is used, and when the ball end mill BM is used, the offset vector As shown in FIG. 10, Can be expressed as a patch From the contact point CO of the cutting edge on the top The center point O existing at a position separated by the radius R _BM of the cutting edge in the direction of is selected as the reference point.

Thus, the offset surface represented by the equations (5) and (6) The tool path data representing the tool path of the ball end mill BM is created based on the curved surface data of the ball end mill BM, and the tool path data is input to an NC milling machine and an NC milling machine which is a control device of the ball end mill BM. O
Is an offset surface The ball end mill BM can be controlled to move on a curved surface represented by Is formed by cutting a free-form surface representing the following.

By the way, the ball end mill BM is actually used as a tool.
In addition to the cutting edge portion of the predetermined radius R _BM , the shaft portion having a predetermined length from the tip is also provided with a cutting edge, and therefore, cutting using the cutting edge of the shaft portion can be performed. It has been made like that.

However, the patch to be cut When it has a shape that stands almost in the Z-axis direction, the shaft part may come into contact with the cutting object before the cutting edge of the ball end mill BM, and as a result, it is possible to avoid the possibility of damaging the ball end mill. There was a problem that I could not get.

In such a case, a free-form patch Based on this, the free-form surface machining data representing the moving path of the upper end of the cutting edge of the shaft portion of the ball end mill BM is generated, and based on this free-form surface processing data, the moving path of the upper end of the cutting edge of the ball end mill BM is calculated. If it can be detected, CAD / CAM
It is thought that the usefulness of the entire system can be significantly improved.

The present invention has been made in view of the above points, and it is an object of the present invention to propose a free-form surface machining data creation method capable of generating free-form surface machining data representing a moving path of the upper end of a cutting edge of an end mill using a free-form surface patch. Is what you do.

E. Means for Solving the Problem In order to solve such a problem, in the present invention, a plurality of patches are provided. As a cutting target free-form surfaces had it occurred formed in, the end mill BM (FM, RM) when cutting using a cutting blade upper CP ₀ end mill BM (FM, RM) of (CP _1, CP ₂₎ Free-form surface machining data representing the moving path A patch representing a free-form surface Unit vector N _{(u, v)} and end mill BM
Offset vector for patch S _{(u, v)} based on the cutting edge shape of (FM, RM) And its offset vector From the end, the center axis O of the end mill BM (FM, RM)
_BM (O _FM, O _RM) first linear vector directed to (L _FM,
L _RM ) and its first straight line vector Central axis O _BM (O _FM from the tip of the end mill BM (FM, RM),
O _RM ) direction, the second straight line vector toward the top edge of the cutting edge of the end mill BM (FM, RM) And the second straight line vector From the tip of the cutting edge of the end mill BM (FM, RM) to the upper end CP ₀ (C
Third straight line vector towards P ₁ , CP ₂ ) Is calculated and the offset vector First, second and third straight line vectors Using a patch Cutting the top end CP ₀ (CP ₁ of the end mill BM (FM, RM) in response to,
Free-form surface machining data representing the travel path of CP ₂ ) The cutting edge formed on the outer peripheral surface from the tip of the end mill BM (FM, RM) to the cutting edge upper end CP ₀ (CP ₁ , CP ₂ ) does not damage the cutting edge. , Cutting products.

F action Patch representing free-form surface Cutting the top end CP ₀ (CP ₁ of the end mill BM (FM, RM) in response to,
Free-form surface machining data representing the travel path of CP ₂ ) , A patch representing a free-form surface The movement limit of the end mill BM (FM, RM) with respect to the end mill BM (FM, RM) can be detected, and the end mill BM (FM, RM) can be prevented from being damaged.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a CAD / CAM system as a whole, which includes a free-form surface creating device 2 including a central processing unit (CPU), a free-form surface cutting tool path creating device 3, and an NC milling machine (machining center) 4. It is composed of

The free-form surface creation device 2 is a free-form surface patch that represents the external shape of a product using the CAD method described above. Generate

The tool path creating device 3 for cutting a free-form surface includes a patch generated by the free-form surface creating device 2. Free-form surface data DT _S made of is inputted, the free based on the surface data DTs, offset curved surface for example, a ball end mill BM as a tool Create and thereby create a'll go-between tool path data DT _CL to the method of segment height method or the like.

Further, in the NC milling machine 4, the movement of the ball end mill BM is controlled based on the tool path data DT _CL inputted through the floppy disk 5 to cut a product having a free-form surface. It has been made executable.

The free-form surface cutting tool path creating device 3 includes a display device 6 composed of a display and an input device 7 composed of, for example, a keyboard and a mouse. The designer looks at a menu screen displayed on the display device 6 while viewing the input device 7. Is operated, the CPU executes the cutting limit plane data creation processing procedure SP1 shown in FIG.

That is, the CPU of the tool path creating device 3 for free-form surface cutting
When the designer instructs the creation of cutting limit surface data at the time of free-form surface cutting by operating the input device 7, the process enters from the cutting limit surface data creation processing procedure SP1 and proceeds to the next step SP2. A free-form patch representing the external shape of the product The free-form surface data DT _S made of, read from sculptured surface generating device 2.

Here, CPU is configured to store the free-form surface data DT _S in the internal memory, sent to the display device 6 as display data DT _DSP, Patsuchi of the free-form surface that represents the outer shape of the product for this result cutting target Displayed on the screen.

Next, the CPU moves to step SP3, where the ball end mill is used.
The cutting edge radius r _BM and the cutting edge length l are specified as the specifications of the cutting edge CL ₀ of _BM.
Wait for _CL0 input.

The ball end mill BM as a tool has, for example, a cylindrical shape having a predetermined shaft radius R _BM as shown in FIG. 3 (A), and has a predetermined cutting edge radius r _BM (= axis) and has a cutting edge CL ₀ radius R _BM), comprising a cutting edge CL ₀ circumferentially portion of _CL0 minutes predetermined cutting length l from the tip.

Here, the designer uses the keyboard of the input device 7 to change the cutting edge radius r _BM and cutting edge length l _{CL0 of the} ball end mill BM.
If the numeric input, CPU takes the input data DT _IN in the internal register, and then proceeds to the following step SP4.

In this step SP4, the CPU waits for the designation input of the finishing margin δ when cutting with the ball end mill BM for the external shape of the product after the cutting process, and in this state, as in step SP3 described above, the designer If the user inputs a desired value of the finishing allowance δ numerically using the keyboard of the input device 7, CP
U takes this input data DT _IN into an internal register.

Subsequently, as shown in FIG. 4, the CPU uses the cutting edge radius r _BM and the cutting edge length l _{CL0 of the} ball end mill BM taken into the internal register as described above, and the finishing allowance δ at the time of cutting. In the next step SP5, the following equation The upper end of the cutting edge of the ball end mill BM to the reference point CP
_0, by the reference point CP ₀ calculates the curved surface to be moved, the cutting limitation surface data Generate

The first to third terms on the right side of the equation (8) are patches of a free-form surface representing the outer shape of the product. Its normal vector to In the direction, and the cutting edge radius r of the ball end mill BM
Offset vector offset by _BM Represents

In addition to this, the fourth term on the right side of the expression (8) is a unit vector in the Z-axis direction. And the offset vector From the tip of the ball end mill BM to the center axis O _BM of the ball end mill BM toward the upper edge of the cutting edge of the ball end mill BM Represents

Further, the fourth term on the right side of equation (8) is A horizontal unit vector parallel to the X and Y axes _Is multiplied by the radius R _BM of the ball end mill BM to obtain a second linear vector Straight line vector from the tip of to the reference point CP ₀ at the upper end of the cutting edge, which is the circumferential portion of the upper end face of the cutting edge of the ball end mill BM Represents

Thus, the right side of the expression (8) as a whole represents the position vector of the reference point CP ₀ in the three-dimensional space, and thus the reference point CP which is the upper end of the cutting edge of the balloon end mill BM.
₀ is the cutting surface data by calculating the curved surface to be moved Can be generated.

In addition, this ball end mill BM ₀ is a free-form patch made of a horizontal plane. When passing over the patch Normal vector Is the unit vector in the Z-axis direction And the outer product is 0, so the horizontal unit vector of equation (9) Becomes 0.

Thus, the cutting limit surface data of the upper end of the cutting edge of the ball end mill BM ₀ described above with respect to the equation (8) Next formula A patch of free-form surface as represented by Above, the finishing margin δ and the cutting edge length l _{CL0 of the} ball end mill BM ₀
It can be seen that only the curved surface shape is offset.

In this step SP5, the CPU uses the cutting end surface data of the upper end of the cutting edge of the ball end mill BM. Is generated and transmitted to the display device 6 as the display data DT _DSP , and the process proceeds to the next step SPK6, where the cutting limit plane data creation processing procedure SP1 is completed.

Thereby, a free-form patch representing the outer shape of the product to be cut is displayed on the screen of the display device 6. Cutting limit surface data generated in the cutting limit surface data creation processing procedure SP1 Is displayed.

Thus, the designer looks at the screen of the display device 6,
Free-form patch And cutting limit surface data By confirming the presence or absence of a cut part, a patch representing a free-form surface when using a ball end mill BM The movement limit of the cutting edge CL ₀ of the ball end mill BM with respect to the tool can be detected, and the tool path data DT _CL can be changed according to the detection result.
BM damage can be prevented beforehand.

According to the above method, the patch of a free-form surface Surface data representing the cutting surface of the cutting edge when using a ball end mill BM Can be easily generated.

In the above-described embodiment, when the ball end mill BM is used for cutting, the cutting limit surface data representing the cutting limit surface of the cutting edge of the ball end mill BM. However, the present invention is not limited to this, and the cutting limit surface data representing the cutting limit surface of the cutting edge when another end mill such as a flat end mill or a radius end mill is attached to the cutting process is used. It can also be applied when generating.

In this connection, as shown in FIG. 3 (B), it has a cylindrical shape whose tip becomes flat, provided with a cutting edge CL ₁ in the circumferential portion of the predetermined length l _CL1 minutes from the flat portion and the tip of the tip flats When the end mill FM is used for cutting, the CPU first determines the axial radius R _FM and the cutting edge of the flat end mill FM as the specifications of the flat end mill FM in step SP3 of the cutting limit plane data creation processing procedure SP1 described above. Requests input of a length l _CL1 .

Subsequently, the CPU uses the shaft radius R _FM and the cutting edge length l _{CL1 of the} flat end mill FM and the finishing margin δ to perform the next step SP5.
In the following equation Based on the cutting edge of the flat end mill FM
As CP _1, by the reference point CP ₁ calculates the curved surface to be moved, the cutting limitation surface data Generate

The first to third terms on the right side of the equation (11) are patches of a free-form surface representing the outer shape of the product. And its normal vector Finish margin δ and shaft radius R _{FM of} flat end mill _FM
Offset vector offset by minutes Represents

In addition to this, the fourth term on the right side of the equation (11) is a horizontal unit vector. Against the normal vector The offset vector represented by the following equation: R _FM −R _FM · sin θ (12) By multiplying the distance to the axis O _FM hula bract end mill FM from the tip off excisional vector No. 1 from the tip of the shaft to the axis O _FM of the flat end mill FM
Straight line vector Represents

Further, the fifth term on the right side of the equation (11) is a first linear vector represented by the following equation: l _CL1 −R _FM · cos θ (13) The distance from the tip of the to the top edge of the cutting edge is the unit vector in the Z-axis direction. By multiplying the first linear vector Second straight line vector from the tip of the end to the upper end face of the cutting edge in the direction of the center axis O _{FM of the} flat end mill FM Is calculated.

Further, the sixth term on the right side of the equation (11) is a horizontal unit vector. Is multiplied by the radius R _FM of the flat end mill FM to obtain a second linear vector. From the tip, the third straight line vector directed to the reference point CP ₁ of the cutting edge upper end consisting of a circumferential portion of the cutting edge upper end surface of the hula bract end mill FM Thus, the right side of equation (11) is expressed as
Represents the position vector of the reference point CP ₁ in the 3-dimensional space, thus, by the reference point CP ₁ made by cutting the upper end of the hula bract end mill FM calculates the curved surface to be moved, the cutting limitation surface of the hula bract end mill FM data Can be calculated.

Alternatively, as shown in FIG. 3 (C), a predetermined radius R _RM (so-called “medium radius”) having a flat tip is used.
Of a predetermined radius r _RM
Which has a cutting edge CL ₂ (so-called minor radius), when using the radius end mill RM with a cutting edge CL ₂ in the circumferential portion of predetermined length l _CL2 minutes from the tip to the cutting, CPU
First, as described above, the cutting limit surface data creation processing procedure SP
In step SP3 of 1, numerical values of the cutting edge length l _CL2 , the media radius R _RM, and the minor radius r _RM of the radius end mill RM are requested as the specifications of the radius end mill RM.

Subsequently, the CPU sets the specified radius end mill R
Using the cutting edge length l _{CL2 of} M, the media radius R _RM and the minor radius r _RM, and the finishing margin δ, in the next step SP5, Based on the cutting edge of the radius end mill RM
As CP _2, by which the reference point CP ₂ calculates the curved surface to be moved, the cutting limitation surface data Generate

The first to third terms on the right side of the equation (14) are patches of a free-form surface representing the outer shape of the product. And its normal vector Offset vector offset by finishing margin δ and minor radius r _RM of radius end mill RM in the direction Represents

In addition to this, the fourth term on the right side of the equation (14) is a horizontal unit vector. Radius end mill RM
Offset vector by multiplying the difference between _RM and minor radius r _RM No. 1 from the tip of the shaft to the axis O _RM of the radius end mill RM
Straight line vector Is calculated.

Further, the fifth term on the right side of the equation (14) is the first straight line vector calculated in the fourth term. The distance from the tip of the to the top edge of the cutting edge is the unit vector in the Z-axis direction. By multiplying the first linear vector Second straight line vector extending from the tip to the central axis O _RM direction of the radius end mill RM the cutting edge upper end surface Is calculated.

Further, the sixth term on the right side of the equation (14) is a horizontal unit vector. Radius end mill RM
By multiplying by _RM , the second linear vector Linear vector from the tip, the third toward the cutting edge upper reference point CP ₂ of comprising the circumferential portion of the cutting edge upper end surface of the radius end mill RM of In this way, the right side of the equation (14) expresses the position vector of the reference point CP ₂ in the three-dimensional space as a whole. Thus, the reference point CP _{2 which} is the upper end of the cutting edge of the radius end mill RM moves. By calculating the surface to be calculated,
Cutting end surface data of radius end mill RM Can be calculated.

In the above-described embodiment, when the cutting limit surface data of the upper end of the cutting edge of the end mill is created, the finishing allowance δ in addition to the specifications of the end mill is specified and input by the designer. The present invention is not limited to this, and a value set in advance may be used as the finishing allowance δ, and even if the finishing allowance δ is not used, the same effect as in the above-described embodiment can be realized.

In the above-described embodiment, the cutting edge of the end mill is
3-axis control type mounted so as to face downward in the Z-axis direction
Although the case where the NC milling machine is used has been described, the edge direction of the end mill is not limited to these. For example, the same effect as that of the above-described embodiment can be realized by using an NC milling machine having a configuration that can be arbitrarily changed.

H Effects of the Invention As described above, according to the present invention, a free curved surface machining data creation method capable of easily generating free curved surface machining data representing a moving path of the upper end of a cutting edge of an end mill according to a patch representing a free curved surface is realized. Thus, by being able to detect the limit of movement of the upper end of the cutting edge of the end mill with respect to the patch representing the free-form surface, breakage of the end mill can be prevented.

Thus, the usefulness as a CAD / CAM system can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of a CAD / CAM system to which a method for creating free-form surface machining data according to one embodiment of the present invention is applied, and FIG. 2 is cutting limit surface data according to the method for creating free-form surface machining data according to the present invention. FIG. 3 is a schematic diagram illustrating an end mill and a cutting edge length, FIG. 4 is a schematic diagram illustrating a principle of a free-form surface machining data generating method using a ball end mill, FIG. FIG. 6 is a schematic diagram showing the principle of a free-form surface machining data creation method using a flat end mill, FIG. 6 is a schematic diagram showing the principle of a free-form surface machining data creation method using a radius end mill, and FIG. FIG. 8 is a schematic diagram illustrating a condition of continuation of a tangent plane, FIG. 9 is a schematic diagram illustrating an offset vector, and FIG. 10 is a free-form surface cut by a ball end mill. Show processing It is a schematic diagram. 1. CAD / CAM system 2. Free-form surface creation device 3.
………………………………………………………………………………………………………………………………………………………….
Flat end mill, RM… Radius end mill,

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G05B 19/4093

Claims (1)

(57) [Claims] When cutting is performed using an end mill with a free-form surface formed by a plurality of patches as a cutting target, free-form surface processing data representing a moving path of an upper end of a cutting edge of the end mill is freely generated. In the curved surface machining data creation method, an offset vector for the patch is calculated based on a unit vector in the normal direction of the patch representing the free-form surface and a cutting edge shape of the end mill, and from the tip of the offset vector, Calculating a first linear vector heading toward the center axis of the end mill, and a second linear vector heading from the tip of the first linear vector toward the upper end surface of the cutting edge of the end mill in the center axis direction of the end mill.
And a third straight line vector from the tip of the second straight line vector toward the upper end of the cutting edge of the end mill is calculated, and the offset vector, the first, second and third straight line vectors are calculated. By using a linear vector to generate free-form surface processing data representing the moving path of the upper end of the cutting edge of the end mill in accordance with the patch, the cutting formed on the outer peripheral surface from the end of the end mill to the upper end of the cutting edge is generated. A method for creating free-form surface machining data, comprising cutting a product so that the cutting edge is not damaged by the blade.