METHOD OF PREPARING NC DATA FOR CUTTING

Abstract: Regions (ZN₁ - ZN₃) are partitioned by horizontal and vertical axes passing through a point (Q) specified by a safe position coordinate value (Z S ) in a longitudinal direction of a blank (WK) and a safe position coordinate value (X S ) in an orthogonal direction to the former. Various approach/escape patterns are in advance stored in accordance with which of the regions described above a turret turning point (P T ) exists in and which one of the plane in the longitudinal direction (LPS) of the blank and the plane in the orthogonal direction (TPS) thereto the cutting start/end point (P S ) belongs to. A predetermined pattern is selected from these stored approach/escape patterns on the basis of the region to which the turret turning point (P T ) actually belongs and off the plane to which the cutting start/end point (P S ) actually belongs, and NC da­ ta for approach and that for escape are prepared by use of the selected pattern.

Description: This invention relates to a method of creating NC data for machining and, more particularly, to an NC data creation method well suited for creating approach and withdrawal NC data in machining. 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 T of a turret TR, the tool is then made to approach a cutting starting point P 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moved along a commanded path at the completion of the approach operation to machine a workpiece WK, and the tool is withdrawn from a cutting end point (which coincides with the cutting starting point) P A to the turret index position P T at the completion of machining performed by the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 A is a point located at a distance Δd from a starting point P 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 T and the cutting starting point P A as the respective starting and end points (see a first approach path PTA₁), and a case (ii) where a suitable transit point (e.g., a point P AA or P AS ) is entered and this point is traversed (see second and third paths PTA₂, PTA₃). 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. EP-A-0137047 discloses a method of determining a three-dimensional tool space according to the preamble of the attached claim 1, wherein a transit point as mentioned must be specified, and wherein the machining operation is a milling operation. According to the present invention there is provided a method of machining a workpiece including creating NC machining data defining an approach path pattern and a withdrawal path pattern for a tool (T L ) relative to a workpiece (WK), comprising registering in advance a plurality of such path patterns (Figs. 3 to 8) and then selecting one of said path patterns for creating said NC data, being a path pattern along which the tool (T L ) will not interfere with an obstacle such as a stationary portion of the machine tool or the workpiece (WK), the method being characterised by: the NC data being for a turning operation and the registered approach/withdrawal path patterns (Figs. 3 to 8) being defined in dependence upon a combination of a particular zone (ZN), in which a tool-holding turret index point (P T ) may be present, and a plane to which a cutting starting/end point (P A ) belongs, the zone (ZN) being one among a plurality of zones (ZN 1,2,3 ) defined by horizontal and vertical axes passing through a point (Q) specified by a safe position coordinate (Z S ) in a longitudinal direction of the workpiece (WK) and a safe position coordinate (X S ) in a direction perpendicular to said longitudinal direction, and the plane being either a plane (LPS) in the longitudinal direction of the workpiece (WK) or a plane (TPS) perpendicular to the longitudinal direction, depending upon to which face of the workpiece the cutting starting/end point (P A ) belongs; selecting a path pattern from among said registered approach/withdrawal path patterns (Figs. 3 to 8) in dependence upon the particular combination of the zone (ZN) to which the turret index point (P T ) actually belongs for the particular turning operation concerned, and the plane (LPS or TPS) to which the cutting starting/end point (P A ) actually belongs for the particular turning operation concerned; creating NC data for approach and NC data for withdrawal using said selected path patter; and machining the workpiece in dependence upon the created NC data. By the expression "safe position coordinate" (Z S ,X S ) it is meant that, in a case where the cutting starting/end point (P 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 A ), or even if the tool is moved vertically away from the cutting starting/end point (P A ), in a danger zone (ZN O ) defined between the safe position coordinates (Z S ,X S ) and the point (Q). Further, in a case where the cutting starting/end point (P A ) resides on an end face perpendicular plane (TPS), the tool will not interfere with an obstacle even if the tool is moved horizontally toward the cutting starting/end point (P A ), or even if the tool is moved horizontally away from the cutting starting/end point (P A ), in the danger zone (ZN O ). For a better understanding of the invention and to show how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: 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 through 8 are views of approach/withdrawal patterns for various cases; Fig. 9 is a flowchart of processing accordinc 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 S a safe position coordinate in the longitudinal direction of the workpiece, X S a safe position coordinate in a direction perpendicular to the longitudinal direction of the workpiece, P A a cutting starting/end point, P T a turret index position, ZN₀ -ZN₃ 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 T is present, the zone being one among the zones ZN₁ - ZN₃ defined by horizonal and vertical axes passing through a point Q (Z S ,X S ) specified by the safe position coordinate Z S in the longitudinal direction of the workpiece and the safe position coordinate X S in the direction perpendicular to the longitudinal direction, and in dependence upon a plane to which the cutting starting end/point P 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 ZN₂ to which the turret index point P T actually belongs and the plane LPS to which the cutting starting/end point P 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 through 8, which are views for describing the approach/withdrawal patterns, show six respective cases in conformance with the turret index P T and cutting starting/end point P A ; three types of pattern are set for each case. More specifically, three approach/withdrawal patterns are set and registered on the floppy FL, as shown in Figs. 3 through 8, for respective ones of six cases conforming to combinations of the area in which the turret index position P T resides, which area is from among the areas ZN₁ - ZN₃ defined by horizonal and vertical axes passing through the point Q specified by the safe position coordinate Z S in the longitudinal direction of the workpiece and the safe position coordinate X 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 A belongs. Fig. 3 is for a case where the turret index point P T belongs to the first zone ZN₁ and the cutting starting/end point P 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 T to a point just above the cutting starting/end point P A , and subsequently lowering the tool to the cutting starting/end point P A , and which, in a Withdrawal operation, 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 T to a boundary point P D , of a danger zone ZN₀, just above the cutting starting/end point P A , and subsequently lowering the tool to the cutting starting/end point P A , and which, in a withdrawal operation, 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 T to a boundary point P D ′ of the danger zone ZN₀, then moving the tool at rapid-traverse to a boundary point P D along the boundary line and subsequently lowering the tool to the cutting starting/end point P A , and which, in a withdrawal operation, is for withdrawing the tool in the direction opposite that of the approach. Fig. 4 is for a case where the turret index point P T belongs to the second zone ZN₂ and the cutting starting/end point P A belongs to the longitudinal plane LPS. Fig. 5 is for a case where the turret index point P T belongs to the third zone ZN₃ and the cutting starting/end point P A belongs to the longitudinal plane LPS. Fig. 6 is for a case where the turret index point P T belongs to the first zone ZN₁ and the cutting starting/end point P A belongs to the end face plane TPS. Fig. 7 is for a case where the turrent index point P T belongs to the second zone ZN₂ and the cutting starting/end point P A belongs to the end face plane TPS. Fig. 8 is for a case where the turret index point P T belongs to the third zone ZN₃ and the cutting starting/end point P A belongs to the end face plane TPS. Three approach/withdrawal patterns are set for each of the Figs. 4 through 8, just as in the case of Fig. 3, 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 S , X S (see Fig. 1) along the respective axes are entered from the keyboard 12 or the like (step 101). The safe position coordinates Z S , X S mean that, in a case where the cutting starting/end point P 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 A , or even if the tool is moved vertically away from the cutting starting/end point P A , in the danger zone ZN₀ specified by Z S , X S . Further, in a case where the cutting starting/end point P 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 A , or even if the tool is moved horizontally away from the cutting starting/end point P A , in the danger zone ZN₀. At the completion of entry of the safe position, a prompt appears calling for the turret index position P T (step 103). Therefore, the coordinates (Z T ,X 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 S , X S along the respective axes and the coordinates Z T , X T of the turret index position P T to determine the zone to which the turret index position P T belongs (step 107), and determines, from the starting point P S of the part profile PFG, the plane to which the cutting starting/end point P A belongs (step 109). If the starting point P S of the part profile PFG resides on the longitudinal surface of the workpiece WK, the cutting starting/end point P A will lie at a position located a distance Δd (already known) directly above the starting point P S and therefore will belong to the longitudinal plane LPS. If the starting point P S resides on the end face of the workpiece WK, the cutting starting/end point P A will lie at a position located a distance Δd′ (not shown) from the starting point P 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 T belongs and the plane to which the cutting starting/end point P 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 T ,X T ) of the turret index point P T , the coordinates Z S , X S of the safe position and the coordinates of the cutting starting/end point P 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 A belongs, which point is located at the position a predetermined distance from the starting point P 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 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 horizonal 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.

Claims: A method of machining a workpiece including creating NC machining data defining an approach path pattern and a withdrawal path pattern for a tool (T L ) relative to a workpiece (WK), comprising registering in advance a plurality of such path patterns (Figs. 3 to 8) and then selecting one of said path patterns for creating said NC data, being a path pattern along which the tool (T L ) will not interfere with an obstacle such as a stationary portion of the machine tool or the workpiece (WK), creating NC data for approach and NC data for withdrawal using said selected path pattern, and machining the workpiece in dependence upon the created NC data, the method being characterised by: the NC data being for a turning operation and the registered approach/withdrawal path patterns (Figs. 3 to 8) being defined in dependence upon a combination of a particular zone (ZN), in which a tool-holding turret index point (P T ) may be present, and a plane to which a cutting starting/end point (P A ) belongs, the zone (ZN) being one among a plurality of zones (ZN 1,2,3 ) defined by horizontal and vertical axes passing through a point (Q) specified by a safe position coordinate (Z S ) in a longitudinal direction of the workpiece (WK) and a safe position coordinate (X S ) in a direction perpendicular to said longitudinal direction, and the plane being either a plane (LPS) in the longitudinal direction of the workpiece (WK) or a plane (TPS) perpendicular to the longitudinal direction, depending upon to which face of the workpiece the cutting starting/end point (P A ) belongs; and selecting a path pattern (any one of Figs.3 to 8) from among said registered approach/withdrawal path patterns (Figs. 3 to 8) in dependence upon the particular combination of the zone (ZN) to which the turret index point (P T ) actually belongs for the particular turning operation concerned, and the plane (LPS or TPS) to which the cutting starting/end point (P A ) actually belongs for the particular turning operation concerned. A method of machining a workpiece including creating NC machining data for turning according to claim 1, characterized by: determining a zone (ZN) to which the turret index point (P T ) belongs using an entered safe position coordinate (Z S ) in the longitudinal direction, a safe position coordinate (X S ) in the direction perpendicular to the longitudinal direction, and data indicative of the turret index position; and determining a plane (LPS, TPS) to which the cutting starting/end point (P A ) belongs from entered part profile data. A method of machining a workpiece including creating NC machining data for turning according to claim 1 or 2, characterized in that when two or more approach withdrawal patterns are registered for each combination of a zone (ZN) to which the turret index point (P T ) belongs and a plane (LPS, TPS) to which the cutting starting/end point (P A ) belongs, and it is specified which pattern of said two or more approach/withdrawal patterns is to be used to create the NC data for approach and withdrawal, a pattern used in creating the NC data for approach and withdrawal is based on the zone (ZN) to which the turret index point (P T ) actually belongs, the plane (LPS, TPS) to which the cutting starting/end point (P A ) actually belongs and said entered pattern selection data. A method of machining a workpiece including creating NC machining data for turning according to claim 3, characterized in that two or more approach/withdrawal patterns conforming to a combination of a zone (ZN) to which the turret index point (P T ) belongs and a plane (LPS, TPS) to which the cutting starting/end point (P A ) belongs is displayed on a display screen (13). A method of machining a workpiece including creating NC machining data for turning according to any preceding claim , characterized in that in a case where a zone in which a workpiece (WK) is present is a danger zone (ZN₀) and the cutting starting/end point (P A ) is present on the plane (LPS) in the longitudinal direction of the workpiece (WK), each of said patterns has a portion for approaching or withdrawing from the cutting starting/end point (P A ) in a vertical direction within the danger zone (ZN₀), and that in a case where the cutting starting/end point (P A ) is present on an end face plane of the workpiece (WK), each of said patterns has a portion for approaching or withdrawing from the cutting starting/end point (P A ) in a horizontal direction within the danger zone (ZN₀).

Inventors: NAKAJIMA MASATOSHI FANUC DAI-, SEKI MASAKI, TAKEGAHARA TAKASHI, NAKAJIMA, MASATOSHI FANUC DAI-3 VIRAKARAMATSU, SEKI, MASAKI, TAKEGAHARA, TAKASHI
Applicants: FANUC LTD, FANUC LTD.
Application year: 1988
Main classification: G05B19
IPC codes: G05B19, B23Q15, B23B1