Method of Creating NC Data for Turning

1. Technical Field

This invention relates to a method of creating NC data for turning and, more particularly, to an NC data creation method well, suited for creating approach and withdrawal NC data for turning.

2. Background Art

In turning performed by a lathe, as shown in FIG. 10, a desired tool TL is selected at an index position (turret index point) P.sub.T of a turret TR. The tool is then made to approach a cutting starting point P.sub.A (see the path indicated by the black arrows). The tool is subsequently moved along a commanded path at the completion of the approach operation so as to machine a workpiece WK. The tool is then withdrawn from a cutting end point (which coincides with the cutting starting point) P.sub.A to the turret index position P.sub.T at the completion of machining performed by the tool (see the white arrows), thereby ending the turning cycle for one process. Thereafter, the tool for the next process is selected and the same operations are repeated, whereby a desired part profile PFG (see the dashed line) is eventually obtained. In FIG. 10, CHK denotes a chuck. The cutting starting/end point P.sub.A is a point located at a distance .DELTA.d from a starting point P.sub.S on the part profile PFG.

With regard to the approach path among the tool paths traversed in such a turning operation, there is a case (i) where a direct approach is made by rapid-traverse positioning using the machining starting point (turret index point) P.sub.T and the cutting starting point P.sub.A as the respective starting and end points (see a first approach path PTA.sub.1), and a case (ii) where a suitable transit point (e.g., a point P.sub.AA or P.sub.AS) is entered and this point is traversed (see second and third paths PTA.sub.2, PTA.sub.3). The same is true for the withdrawal path. It should be noted that the cutting path is automatically decided by entering the part profile.

When the direct approach or withdrawal of case (i) is made, the approach and withdrawal distances can be shortened but a problem which arises is that the tool may be obstructed by obstacles such as a stationary portion of the machine, the workpiece, etc.

When approach or withdrawal is made so as to traverse the designated transit point as in case (ii), it can be arranged so that the tool will not interfere with the workpiece, but the transit point for the approach or withdrawal must be designated each time the approach or withdrawal is performed. This is a troublesome operation.

Accordingly, an object of the present invention is to provide a method of creating NC data for turning, wherein an approach path and withdrawal path which will not cause interference with an obstacle can be decided without entering a transit point.

In a method of creating NC data for turning according to the present invention, various approach/withdrawal patterns are registered in dependence upon a particular zone in which a turret index point is present, the zone being one among zones defined by horizontal and vertical axes passing through a point specified by a safe position coordinate in a longitudinal direction of a workpiece and a safe position coordinate in a direction perpendicular to the longitudinal direction, and in dependence upon a plane to which the cutting starting/end point belongs, the plane being one of a plane in the longitudinal direction of the workpiece and a plane perpendicular to the longitudinal direction. A predetermined pattern is selected from among the registered approach/withdrawal patterns based on the zone to which the turret index point actually belongs and the plane to which the cutting starting/end point actually belongs. NC data for approach and NC data for withdrawal are created using the selected pattern .

FIG. 1 is a view for describing the principle of the NC data creation method of the present invention;

FIG. 2 is a block diagram of a system for executing the method of the invention;

FIGS. 3(a) through 8(c) are views of approach/withdrawal patterns;

FIG. 9 is a flowchart of processing according to the invention; and

FIG. 10 is a view for describing paths used in a lathe.

FIG. 1 is a view for describing the principle of the NC data creation method of the present invention. WK represents a workpiece, PFG (the dashed line) a part profile, Z.sub.S a safe position coordinate in the longitudinal direction of the workpiece, X.sub.S a safe position coordinate in a direction perpendicular to the longitudinal direction of the workpiece, X.sub.A a cutting starting/end point, P.sub.T a turret index position, ZN.sub.0 -ZN.sub.3 zones, LPS a plane (longitudinal plane) parallel to the longitudinal direction of the workpiece, and TPS a plane parallel to the end face of the workpiece.

Various approach/withdrawal patterns are registered in dependence upon a particular zone in which the turret index point P.sub.T is present. The zone is one of the zones ZN.sub.1 -ZN.sub.3 defined by horizontal and vertical axes passing through a point Q (Z.sub.S,X.sub.S) specified by the safe position coordinate Z.sub.S in the longitudinal direction of the workpiece and the safe position coordinate X.sub.S in the direction perpendicular to the longitudinal direction. The zone is selected in dependence upon a plane to which the cutting starting end/point P.sub.A belongs, the plane being one of the plane (longitudinal plane) LPS in the longitudinal direction of the workpiece and the plane (end face) TPS perpendicular to the longitudinal direction. A predetermined pattern is selected from among the registered approach/withdrawal patterns based on a combination of the zone ZN.sub.2 to which the turret index point P.sub.T actually belongs and the plane LPS to which the cutting starting/end point P.sub.A actually belongs. NC data for approach and NC data for withdrawal are created using the selected pattern.

FIG. 2 is a block diagram of an automatic programming system for practicing the method of creating NC data for turning according to the present invention. Numeral 11 denotes the main body of the system, which includes a processor (CPU) 11a, a program memory (ROM) 11b for storing a loading program and the like, and a RAM 11c which stores a system program for NC data creation read in from a floppy FL, approach and withdrawal patterns, as well as the results of processing, etc.

Numeral 12 denotes a keyboard, 13 a graphic display unit, 14 a disk controller, and 15 an NC data output unit for outputting created NC data to an external storage medium (NC tape). The floppy FL stores the system program for creating NC data, the approach/withdrawal patterns, etc.

FIGS. 3(a) through 8(c), which are views for describing the approach/withdrawal patterns, show six respective cases in conformance with the turret index P.sub.T and cutting starting/end point P.sub.A ; three types of patterns are set for each case. More specifically, three approach/withdrawal patterns are set and registered on the floppy FL, as shown in FIGS. 3(a) through 8(c). These patterns represent respective ones of six cases for combinations of the area in which the turret index position P.sub.T resides. The area is one of the areas ZN.sub.1 -ZN.sub.3 defined by horizontal and vertical axes passing through the point Q specified by the safe position coordinate Z.sub.S in the longitudinal direction of the workpiece and the safe position coordinate X.sub.S in the direction perpendicular to the longitudinal direction, and the plane (longitudinal plane) LPS in the longitudinal direction of the workpiece or the plane (end face) TPS perpendicular to the longitudinal direction to which the cutting starting/end point P.sub.A belongs.

FIGS. 3(a)-3(c) are for a case where the turret index point P.sub.T belongs to the first zone ZN.sub.1 and the cutting starting/end point P.sub.A belongs to the longitudinal plane LPS. FIG. 3(a) shows a pattern which, in an approach operation, is for moving the tool horizontally, i.e., in the -Z direction, at rapid-traverse from the turret index point P.sub.T to a point just above the cutting starting/end point P.sub.A. The tool is subsequently lowered to the cutting starting/end point P.sub.A. In a withdrawal operation, FIG. 3(a) is for withdrawing the tool in the direction opposite that of the approach. FIG. 3(b) shows a pattern which, in an approach operation, is for moving the tool at rapid-traverse simultaneously along two axes from the turret index point P.sub.T to a boundary point P.sub.D, of a danger zone ZN.sub.0, just above the cutting starting/end point P.sub.A. The tool is subsequently lowered to the cutting starting/end point P.sub.A. In withdrawal operation, FIG. 3(b) is for withdrawing the tool in the direction opposite that of the approach. FIG. 3(c) shows a pattern which, in an approach operation, is for lowering the tool at rapid-traverse from the turret index point P.sub.T to a boundary point P.sub.D ' of the danger zone ZN.sub.0, then moving the tool at rapid-traverse to a boundary point P.sub.D along the boundary line. The tool is subsequently lowered to the cutting starting/end point P.sub.A. In a withdrawal operation, FIG. 3(c) is for withdrawing the tool in the direction opposite that of the approach.

FIGS. 4(a)-4(c) are a case where the turret index point P.sub.T belongs to the second zone ZN.sub.2 and the cutting starting/end point P.sub.A belongs to the longitudinal plane LPS. FIGS. 5(a)-5(c) are for a case where the turret index point P.sub.T belongs to the third zone ZN.sub.3 and the cutting starting/end point P.sub.A belongs to the longitudinal plane LPS. FIGS. 6(a)-6(c) are for a case where the turret index point P.sub.T belongs to the first zone ZN.sub.1 and the cutting starting/end point P.sub.A, belongs to the end face plane TPS. FIGS. 7(a)-7(c) are for a case where the current index point P.sub.T belongs to the second zone ZN.sub.2 and the cutting starting/end point P.sub.A belongs to the end face plane TPS. FIGS. 8(a)-8(c) are for a case where the turret index point P.sub.T belongs to the third zone ZN.sub.3 and the cutting starting/end point P.sub.A belongs to the end face plane TPS. Three approach/withdrawal patterns are set for the FIGS. 4(a) through 8(c), just as in the case of FIGS. 3(a)-3(c) and these patterns are registered on the floppy FL.

FIG. 9 is a flowchart of processing according to the present invention. The method of creating NC data according to the present invention will now be described in accordance with this flowchart. It is assumed that the system program, the approach/withdrawal data and other data have already been transferred to and stored in the RAM 11c from the floppy FL under the control of the loading program stored in the ROM 11b.

In response to start of operation for creating NC data for turning, the graphic display unit 13 displays a prompting screen calling for the safe position coordinates in the Z direction (longitudinal direction of the workpiece) and X direction. Accordingly, the safe position coordinates Z.sub.S, X.sub.S (see FIG. 1) along the respective axes are entered from the keyboard 12 or the like (step 101).

The safe position coordinates Z.sub.S, X.sub.S mean that, in a case where the cutting starting/end point P.sub.A resides on the longitudinal plane LPS, the tool will not interfere with an obstacle even if the tool is moved vertically toward the cutting starting/end point P.sub.A, or even if the tool is moved vertically away from the cutting starting/end point P.sub.A, in the danger zone ZN.sub.0 specified by Z.sub.S, X.sub.S. Further, in a case where the cutting starting/end point P.sub.A resides on the end face plane TPS, the tool will not interfere with an obstacle even if the tool is moved horizontally toward the cutting starting/end point P.sub.A, or even if the tool is moved vertically away from the cutting starting/end point P.sub.A, in the danger zone ZN.sub.0.

At the completion of entry of the safe position, a prompt appears calling for the turret index position P.sub.T (step 103). Therefore, the coordinates (Z.sub.T,X.sub.T) of the point are entered in the same manner (step 103).

Next, the part profile PFG, turning conditions and data indicative of the tool used are entered in the same manner as practiced in the prior art (step 105).

When the entry of the part profile and the like is completed, the processor considers the safe position coordinates Z.sub.S, X.sub.S along the respective axes and the coordinates Z.sub.T, X.sub.T of the turret index position P.sub.T to determine the zone to which the turret index position P.sub.T belongs (step 107), and determines, from the starting point P.sub.S of the part profile PFG, the plane to which the cutting starting/end point P.sub.A belongs (step 109). If the starting point P.sub.S of the part profile PFG resides on the longitudinal surface of the workpiece WK, the cutting starting/end point P.sub.A will lie at a position located a distance .sub..DELTA. d (already known) directly above the starting point P.sub.S and therefore will belong to the longitudinal plane LPS. If the starting point P.sub.S resides on the end face of the workpiece WK, the cutting starting/end point P.sub.A will lie at a position located a distance .sub..DELTA. d' (not shown) from the starting point P.sub.S in the horizontal direction and therefore will belong to the end face plane TPS.

Thereafter, the processor 11a causes the first, second and third approach/withdrawal patterns [e.g., FIGS. 3(a)-(c)] to be displayed in conformity with the combination of the area to which the turret index point P.sub.T belongs and the plane to which the cutting starting/end point P.sub.A belongs, as determined at steps 107, 109. Along which pattern the approach and withdrawal are to be made is entered (step 111). It should be noted that it is not essential to display the patterns.

Using the approach/withdrawal pattern entered at step 111, the coordinates (Z.sub.T,X.sub.T) of the turret index point P.sub.T, the coordinates Z.sub.S, X.sub.S of the safe position and the coordinates of the cutting starting/end point P.sub.A, the processor 11a automatically creates NC data for the approach (step 113), creates NC data for the cutting path using the part profile data, machining conditions, etc., after creation of the NC data for approach (step 115), and finally creates NC data for the withdrawal in the direction opposite that of the approach, after which processing is ended (step 117).

The foregoing description is rendered upon taking into consideration the plane to which the cutting starting/end point P.sub.A belongs, which point is located at the position a predetermined distance from the starting point P.sub.S of the part profile. However, it is permissible to adopt an arrangement in which the approach/withdrawal pattern is decided in a similar manner upon taking into consideration the plane to which the starting point P.sub.S belongs.

Further, the foregoing description pertains to an arrangement in which three approach/withdrawal patterns exist for each of six cases conforming to the turret index position and the cutting starting/end point. However, the invention is not limited to this arrangement, for it will suffice if only one pattern is provided for each case.

In accordance with the present invention, various approach and withdrawal patterns are registered in dependence upon a combination of a particular zone in which a turret index point is present, the zone being one among zones defined by horizontal and vertical axes passing through a predetermined point, and the longitudinal plane or end face plane to which the cutting starting/end point belongs. NC data for approach and NC data for withdrawal are created using a predetermined pattern from among the registered approach/withdrawal patterns based on the zone to which the turret index point actually belongs and the plane to which the cutting starting/end point actually belongs. As a result, it is possible to simply decide an approach path and withdrawal path which will not cause interference with an obstacle without deciding and entering transit points one at a time for the purpose of avoiding interference with the obstacle, as is required in the prior art.