METHOD OF PREPARING NC DATA FOR CUTTING GROOVES

Abstract: In a method of preparing NC data for cutting grooves, a unit normal vector (N) is found at a position (Pe) at which the groove cutting is finished after the NC data for groove cutting have been prepared, and a displacement vector ( ) is found by the multiplication of a designated displacement (da) and the unit normal vector ( ). Thereafter, NC data for es­ capement are prepared for moving the tool (TL) from the position (Pe) to a point defined by the moving vector ( ).

Description: Technical Field This invention relates to a method of creating NC data for grooving. More particularly, the invention relates to a grooving NC data creation method through which NC data are created for cutting a groove in a three-dimensional curved surface and withdrawing a tool from the three-dimensional curved surface by a designated distance at the end of grooving. Background Art In grooving a curved surface by simultaneous five-axis control, it is required at the end of grooving to withdraw the tool from the position at which cutting ends. To this end, the conventional practice at the time of NC data creation is for the operator to designate a withdrawal point or a widthdrawal distance in which the +Z axis is taken as the withdrawal axis, and NC data is created in such a manner that the tool is withdrawn to the designated withdrawal point or the designated withdrawal distance along the + Z axis. However, when determining a withdrawal point in an arbitrary direction or a withdrawal point at a position that is a designated distance in the +Z direction, a problem that arises is that the tool cuts away a portion of the curved surface of the article at withdrawal. Fig. 8 illustrates a case in which a tool TL is withdrawn from a grooving end point Pe a withdrawal distance f in the +Z direction. At withdrawal, the shaded portion of the three-dimensional curved surface SS is cut away. Accordingly, an object of the present invention is to provide a grooving NC data creation method which makes it possible to simply create NC data which will not cause the curved surface of an article to be cut away at withdrawal of a tool. Disclosure of the Invention In a method of creating NC data for grooving, a unit normal vector ( ) at the position of a grooving end point (Pe) is obtained after creation of NC data for grooving, a movement vector ( ) is obtained by multiplying a designated movement distance (da) by the unit normal vector ( ), and NC data for withdrawal are created for moving a tool, by the amount of the movement vector ( ), from the position at which grooving ends (Pe). Brief Description of the Drawings Fig. 1 is a schematic explanatory view of the method of the present invention; Fig. 2 is a block diagram of an apparatus for practicing the method of the invention; Fig. 3 is a flowchart of processing according to the method of the invention; Fig. 4 is an explanatory view of a groove in a three-dimensional curved surface; Figs. 5 through 7 are explanatory views of a method of computing a normal vector; and Fig. 8 is an explanatory view of the prior-art method. Best Mode for Carrying Out the Invention Fig. 1 is a schematic explanatory view of the method of the present invention, in which SS denotes a three-dimensional curved surface, GR a groove, Pe a position at which grooving ends, TL a tool, Ae a tool nose point corresponding to the grooving end point Pe, Pe' a withdrawal point, da a distance along which the tool is moved from the grooving end point Pe to the withdrawal point Pe', a unit normal vector at the point Pe, and a movement vector for movement from the grooving end point Pe to the withdrawal point Pe'. Fig. 2 is a block diagram of an automatic programming apparatus for practicing the method of the present invention. Numeral 101 denotes a keyboard for data input, 102 a processor, 103 a ROM for storing a control program, 104 a RAM, 105 a working memory, 106 a curved-surface memory for storing grid points of meshes MS specifying the curved surface SS (see Fig. 4), unit normal vectors at the grid points, and NC program data for the curved surface and grooving machining, 107 an output unit for outputting, to an external storage medium 108 such as a paper tape or magnetic tape, created curved surface data or NC program data for curved surface or grooving machining, 109 an address bus, and 110 a data bus. Fig. 3 is a flowchart of processing for creating NC data for grooving in accordance with the present invention, Fig. 4 is a view for describing a groove in a three-dimensional curved surface, and Figs. 5 through 7 are explanatory views of a method of computing a normal vector. The method of the present invention will now be described in accordance with the flowchart of Fig. 3. In Fig. 4, MK represents a groove curve for specifiying a groove on the three-dimensional curved surface. The groove curve MK is obtained as a result of projecting a planar curve CV, which is given on an X-Y plane, onto the curved surface SS. The groove curve MK is actually expressed as a point sequence composed of points of intersection between the meshes MS of the curved surface MS and the curve obtained by projecting the curve CV. It is assumed that position data indicative of each point on the sequence have already been stored in the RAM 104. As for the method of computing the groove curve, refer to Figs. 5 and 6 in the specification of International Application No. PCT/JP88/00159 (filed on February 17, 1988 and entitled "Method of Creating Curved Surfaces"). It is also assumed that the tool movement distance da and groove depth h at the grooving end point have already been entered from the keyboard 101. NC data are created for moving the tool TL to the grooving end point Pe (Fig. 4) along the groove curve MK (step 201). The tool TL is capable of being controlled simultaneously along five axes, namely an X axis, Y axis, z axis, horizontal rotational axis (B axis) and vertical rotational axis (C axis). NC data for simultaneous five-axis control are created in such a manner that the vector of the central axis of the tool will point in the direction of the normal line of the workpiece at each point constituting the groove curve (point sequence) MK. More specifically, letting , represent the normal vectors at mesh grid points Pk1, Pk2, as shown in Fig. 5, a normal vector N at a point MK(j) constituting the groove curve is given by On the basis of the normal vector (let the components thereof along the respective axes be i, j, and k), tool length L and tool nose position (X,Y,Z), the position (x,y,z) of the center of rotation of the tool and the positions (b,c) of horizontal and vertical rotation are computed in accordance with the following well-known computation formulae: x = X + L·i y = Y + L·j z = Z + L·k c = tan⁻¹(j/i) The NC data for simultaneous five-axis control are created using x, y, z, b and c. The tool nose position is that at depth h commanded in the normal direction from a point on the groove curve MK. When the processor 102 ends creation of NC data up to the grooving end point Pe (Fig. 1), the processor calls the point Pe from the RAM 104 and obtains the unit vector at the point Pe (step 202). The unit vector at the grooving end point Pe is obtained through the following procedure described with reference to Figs. 6 and 7: (1) Mesh grid points P(i,j), P(i+1,j), P(i,j+1), P(i+1,j+1) which include the grooving end point Pe are obtained from,the curved surface memory 106. (2) From the aforementioned four points, the points P(i,j), P(i+1,j), P(i+1,j+1), which constitute a triangle that includes the grooving end point Pe, are selected (see Fig. 6). (3) Let S represent the area of the triangle including the grooving end point Pe, and let S0, S1, S2 represent the areas of the triangles each of which has the grooving end point Pe as an apex, as shown in Fig. 7. The unit normal vector at the grooving end point Pe is obtained in accordance with the following equation: using unit normal vectors (i,j), (i+1,j), (i+1,j+1) corresponding to the points P(i,j), P(i+1,j), P(i+1,j+1) called from the curved surface memory 106. Next, the processor 102 uses the unit normal vector and the already entered movement distance da to obtain the movement vector in accordance with the following equation (step 203): and then uses the position vector of the grooving end point and the movement vector to obtain the position vector ' of the withdrawal point in accordance with the following equation (step 204): Thereafter, the position vector ' of the withdrawal point is used to create NC data for moving the tool TL from the grooving end point Pe to the withdrawal point Pe' (step 205). Thus, in accordance with the present invention, the arrangement is such that a unit normal vector at the position of a grooving end point is obtained, a movement vector is obtained by multiplying a designated distance by the unit normal vector, and NC data for withdrawal are created for moving a tool, by the amount of the movement vector, from the position at which grooving ends. As a result, it is possible to simply create NC data which will not cause cut-away at withdrawal of a tool.

Claims: A grooving NC data creation method for creating NC data which causes a tool (TL) to withdraw a designated distance (da) from a three-dimensional curved surface (SS) at the end of grooving of said three-dimensional curved surface (SS), characterized by: creating NC data for performing grooving machining by moving a tool (TL) along a curve (MK) specifying a groove on a three-dimensional curved surface; subsequently obtaining a unit normal vector ( ) at a grooving end point (Pe); obtaining a movement vector ( ) by multiplying the designated movement distance (da) by said unit normal vector ( ) and creating withdrawl NC data for moving the tool (TL), by the amount of and in the direction of the movement vector ( ), from said grooving end point (Pe). A grooving NC data creation method according to claim 1, characterized by adopting, as the groove on said three-dimensional curved surface (SS), a projected curve MK obtained by projecting a curve (CV), which is given on an X-Y plane, onto the three-dimensional curved surface (SS). A grooving NC data creation method according to claim 2, characterized by partitioning the three-dimensional curved surface (SS) by a number of meshes, and adopting a sequence of points, which are formed by points of intersection between said projected curved (MK) and meshes, as the curve specifying said groove. A grooving NC data creation method according to claim 1, characterized by obtaining four grid points of meshes which include the grooving end point (Pe), obtaining three points, from among said four points, constituting a triangle which includes the grooving end point, obtaining an area S of said triangle and areas S0, S1, S2 of respective triangles obtained when said triangle is divided into three triangles each having the grooving end point (Pe) as an apex thereof, and obtaining a normal vector at the grooving end point in accordance with the following equation: when normal vectors at said three points are represented by , , .

Inventors: HANAOKA OSAMU FANUC DAI- VIRAK, SAMUKAWA KOJI FANUC DAI- VIRAK, SEKI MASAKI - - - TAKAIDO-NISH, HANAOKA, OSAMU FANUC DAI-3 VIRAKARAMATSU, SAMUKAWA, KOJI FANUC DAI-3 VIRAKARAMATSU, SEKI, MASAKI 3-15-2-406, TAKAIDO-NISHI
Applicants: FANUC LTD, FANUC LTD.
Application year: 1988
Main classification: G05B19
IPC codes: G05B19