METHOD FOR FORMING CURVED SURFACES

Abstract: The curved surface (WK) having different top and bottom shapes is specified by inputting two curves (CV1,CV2), determining the corresponding points on the two curves and connecting them. The curves (CV1,CV2) are formed of pixels (G1-G5,E1-E9), which are finite straight lines or circular arcs. When a point on one curve corresponds to more than one point on the other curve, their correspondence is specified in a definition statement of an NC program, e.g P1 to E2. Then the pixel (E2) is divided into several segments and all the points (Q1,q11,q12,Q2) on the pixel (E2) are connected to the single point (P1).

Description: This invention relates to a method of creating curved surfaces and, more particularly, to a method of machining the edge surface of a part whose upper and lower surfaces differ in shape. As shown in Fig. 4, a known method of creating a curved edge surface of a part WK whose upper and lower surfaces differ in shape includes inputting first and second curves CV1, CV2, obtaining corresponding points P i , Q i on the first and second curves, and connecting these corresponding points. More specifically, the curved surface of the part WK is created (machined) by obtaining the corresponding point P i , Q i , preparing NC data in such a manner that the corresponding points P i , Q i are traversed simultaneously, and moving a tool BT on the basis of the NC data. Methods of thus creating the curved surface of a part by giving two curves are disclosed in the specification of U.S.P. 4,559,601 "Numerically Controlled Milling Method", the specification of U.S. Serial No. 624,676 "Wire-Cut Taper Machining Method", filed in the U.S.A. on June 19, 1984, and in the specification of U.S. Serial No. 732,010 "Wire Discharge Machining Method", filed in the U.S.A on April 29, 1985 (US 4 703 146). Fig. 5 is a view for describing a conventional method of creating a curved edge surface. CV1 and CV2 denote first and second curves for specifying the shapes of upper and lower surfaces, G₁, G₃, G₅, G₇, ... denote elements on the first curve, and G₂, G₄, G₆, G₈ denote elements on the second curve. The elements G1, G₂; G₃, G₄; G₅, G₆; G₇, G₈;... correspond to each other. In such case, the curves CV1, CV2 and a partitioning pitch (mm) are defined as follows: CV1 = S₁; S₂; C (x₁,y₁,r₁), CW, S₃; S₄; C (x₂,y₂,r₂) CW, S₅;... CV2 = S₆; S₇; C (x₃,y₃,r₃), CW, S₈; S₉; S₁₀;... CUT P,5; S i (i = 1, 2, ...) indicates the end point of a figure element which is a line segment or circular arc, and C a circular arc. The x i ,y i ,z i in the parentheses indicate the center and radius of the circular arc, CW indicates a circular arc in the clockwise direction, and ";" indicates the end of a block. The pitch in a base line direction along the first and second curves is specified by the numerical value following the word address P indicative of the partitioning pitch. When definition statements and partitioning information concerning the first and second curves CV1, CV2 have been entered, an apparatus for creating a curved surface successively calculates corresponding points on the first and second curves and, on the basis of the results of the calculations, creates NC data in such a manner that the corresponding points will be traversed simultaneously. Depending upon the curved surface, there are cases where a curved surface includes an edge portion in which the starting point or terminal point of one element on one of the curves corresponds to all points on at least one element of the other curve. However, the conventional curved surface creation method is such that elements on the first curve always correspond to elements on the second curve and, as a result, a curved surface having the aforementioned edge portion cannot be specified. Accordingly, an object of the present invention is to provide a curved surface creation method through which a curved surface can be created simply and reliably even if the curved surface includes an edge portion in which one point on one curve for specifying the upper or lower surface of a workpiece corresponds to a plurality of points on the other curve. Disclosure of the Invention This invention, which is defined in claim 1, includes a curved surface creation method for creating the part figure, whose upper and lower surfaces differ in shape, by inputting first and second curves specifying the shapes of the upper and lower surfaces of the workpiece, obtaining corresponding points on the first and second curves, and connecting the corresponding points. More particularly, the invention relates to a method of creating a curved surface having a special edge portion. In the present invention, if one point on one curve of first and second curves constituted by figure elements, which are line segments or circular arcs, corresponds to all points on at least one figure element of the other curve, the correspondence between the point on the one curve and the figure element on the other curve is inputted upon being specified in the curve definition statement. Thereafter, the figure element on the other curve corresponding to the point on the one curve is partitioned into a predetermined number of segments, and the edge portion is formed by connecting the point with all of the partitioning points. Further details of the present invention are specified in claim 1. In accordance with this method, a curved surface can be created simply and reliably even if the curved surface includes an edge portion in which one point on one curve for specifying the upper or lower surface of a workpiece corresponds to a plurality of points on the other curve. Brief Description of the Drawings Fig. 1 is a view for describing the general features of the invention, in which Fig. 1A is a perspective view, Fig. 1B is a view showing the shape of an upper surface, and Fig. 1C is a view showing the shape of a lower surface; Fig. 2 is a block diagram of a curved surface creation apparatus for realizing the invention; Fig. 3 is a flowchart of processing according to the invention; and Figs. 4 and 5 are views for describing the background of the invention. In Fig. 1, CV1 denotes a first curve specifying the shape (ie periphery) of the upper surface of a part WK, CV2 denotes a second curve specifying the shape (ie periphery) of the lower surface of the part, G i (i = 1 ∼ 5) denotes a figure element on the first curve, and E j (j = 1 ∼ 9) denotes a figure element on the second curve. It should be noted that the figure elements include linear elements (line segments) and circular arcs. The first and second curves CV1, CV2 are defined by aligning the figure elements G₁ ∼ G₅, E₁ ∼ E₉ in the order of traversal starting from starting points P s , Q s . If a point P₁ on the one curve CV1 corresponds to all points on at least one figure element E₂ (circular arc Q₁Q₂) on the other curve, the correspondence between the point P₁ on the one curve and the figure element E₂ on the other curve will be specified in a curve definition statement. When generating the curved surface, the element E₂ on the other curve corresponding to the point P₁ on the one curve CV1 is partitioned into a predetermined number of segments decided on the basis of separately provided partitioning information, and an edge portion EG1 is formed by connecting the point P₁ and all of the partitioning points Q₁, q₁₁, q₁₂, Q₂. When milling is performed, NC data are created in such a manner that the corresponding points on the first and second curves CV1, CV2 are traversed simultaneously, and a tool is moved on the basis of the NC data to generate the curved surface. Fig. 2 is a block diagram of a curved surface creation apparatus for realizing the invention. Numeral 11 denotes a controller body, 12 a keyboard, 13 a CRT, 14 an input/output unit such as a disc unit, and 15 a floppy disc. The controller body 11 has a processor 11a, a ROM 11b, a RAM 11c and a working memory 11d. Fig. 3 is a flowchart of processing according to the invention. The curved surface creation method of the invention will now be described in accordance with Figs. 1 through 3. (1) The first step is to specify the end points of the elements G i , E i (i = 1, 2,...) forming the first and second curves CV1, CV2, respectively. It should be noted that an end point is the starting point or terminal point of the figure element. Thereafter, curve definition statements specifying the first and second curves CV1, CV2 and the pitch, which is the pitch information, are inputted. The curve definition statement and pitch definition statement are as follows, using Fig. 1 as an example. Note that points P₁, P₂, P₃ and P₄ on the first curve CV1 are assumed to correspond to the figure elements E₂, E₄, E₆ and E₈ on the second curve CV2, respectively. Thus, the definition statement for the first curve CV1 is as follows: The definition statement for the second curve CV2 is as follows: The pitch definition statement is CUT P, 5, 5 In the curve definition statements, MRK s (s = 1 - 8) represents a marking point command indicative of a marking point. Definition is such that a point on one curve including the two marking point commands will correspond to a figure element between two points on the other curve that include the respective marking point commands. For example, since the point P₁ on the first curve CV1 includes the two marking point commands MRK₁, MRK₂, the point P₁ corresponds to the figure element E₂ between the point (marking starting point) Q₁ on the second curve CV2 which includes the marking point command MRK₁ and the point (marking terminal point) Q₂ which includes the marking point command MRK₂. Further, in the curve definition statements, C represents a circular arc, CW the clockwise direction (and CCW the counter-clockwise direction), and x₁, y₁, r₁ within the parentheses represent the center and radius of a circular arc. Pitch in the direction of a driving line is specified by the first numerical value that follows the word address P indicative of partitioning pitch, and pitch in the direction of a base line is specified by the second numerical value. The directions of movement along the first and second curves indicated by the bold lines in Fig. 1A are the base line directions, and the directions (edge directions) indicated by the fine lines are the driving line directions. (2) When the curve definition statements and pitch definition statement have been inputted, the processor 11a obtains the line lengths L 1i , L 2i of each of the figure elements of curves CV1, CV2, and the total line lengths L₁, L₂ of the respective curves CV1, CV2 are calculated. (3) Thereafter, of the curves having the lengths L₁ and L₂, the length of the longest is represented by L and L/P (where P is the pitch) is obtained. An integer nearest to but greater than L/P is adopted as the number of partitions M of the curve having the greatest length (referred as the "long curve"). In Fig. 1, the long curve is the second curve CV2. (4) Next, (L 2j /L)·M is rounded off to obtain the number of partitions M j of each figure element E j of the long curve (the second curve) CV2. (5) When the partitioning number M j has been obtained, the processor reads the data (the starting points P s , Q s of the first and second curves) of the initial block from the curve definition statements of the first and second curves CV1, CV2 and stores these data in the RAM 11c as corresponding starting point data. (6) After the starting point is stored, the operations 1 → i, 1 → j, 0 → F are performed, where F is a flag indicating that a marking point command has been issued. Further, let the initial block of a curve definition statement be a 0th block, the next a 1st block, the one after that a 2nd block, and so on. (7) Thereafter, the i-tb and j-th blocks (i-th and j-th figure elements) of the first and second curve definition statements are read. (8) The processor checks whether a marking point command indicative of a marking starting point is present in the data read. (9) If a marking point command specifying a marking starting point is present, the operation 1 → F is performed. (10) If a marking point command indicating a marking starting point is not present, or after the processing of step (9) has been performed, the i-th and j-th figure elements on the first and second curves are each partitioned into M j segments and the partitioning points on the first and second curves are stored in the RAM 11c in corresponding relationship. Note that M j is the number of partitions of the j-th figure element of the second curve, which is the long curve. (11) When the partitioning points of the i-th and j-th figure elements have been brought into correspondence, it is determined whether the condition flag F = 1 holds. (12) When F = 1 does not hold, the operations i + 1 → i, j + 1 → j are performed. (13) Thereafter, a check is performed to determine whether a block defining a curve remains. If one does remain, processing from step (7) onward is repeated. (14) If the aforementioned block does not remain, it is construed that the points on the first curve and the points on the second curve have been brought into correspondence, and NC data are created for moving a tool (inclusive of a wire in a wire electrical discharge machine) so as to successively traverse the corresponding points obtained. Processing is then ended. (15) If F = 1 is found to hold at step (11), block number j of the long curve (the second curve in the example) is incremented by the operation j + 1 → j. (16) Thereafter, the data in the j-th block (the j-th figure element) is read from the curve definition statement of the long curve (the second curve). (17) This is followed by obtaining the partitioning points on the second curve by partitioning the j-th figure element on the second curve into M j segments, and storing each partitioning point in the RAM 11c upon bringing it into correspondence with the marking starting point on the first curve. In the example of Fig. 1, the 2nd figure element E₂ is partitioned into three segments, and the partitioning points q₁₁, q₁₂, Q₂ are stored in the RAM 11c upon being brought into correspondence with point P₂ on the first curve. (18) Next, it is checked whether the j-th block includes a marking point command indicating a marking terminal point. If the command is not included in the block, processing is repeated from step (15) onward. (19) If the block does include the marking point command indicating the marking terminal point, then the operation 0 → F is performed and processing is executed from step (12) onward. Thus, in accordance with the invention, a curved surface can be created simply and reliably even if the curved surface includes an edge portion in which one point on one curve specifying the upper or lower surface of a workpiece corresponds to a plurality of points on the other curve.

Claims: A method of machining the edge surface of a part having upper and lower surfaces of different peripheral shape, comprising creating NC data defining said edge surface by inputting first and second curves (CV1,CV2) specifying the peripheries of the upper and lower surfaces respectively, obtaining corresponding points (P i ,Q i ) on said first and second curves (CV1,CV2), and connecting the corresponding points on the two curves (CV1,CV2) thereby to define the edge surface to be machined, characterised by comprising: a first step of specifying and inputting, in a curve definition statement, correspondence between a point (P₁) on one curve (CV1) and a figure element (E₂) on the other curve (CV2) in a case where, of first and second curves (CV1,CV2) formed by figure elements which are straight line segments or circular arcs, the point (P₁) on the one curve (CV1) corresponds to all points on at least said figure element (E₂) on the other curve (CV2), wherein the correspondence is specified by using two marking point commands (MRK₁,MRK₂) in each curve definition statement so that a point (P₁) on the one curve (CV1) including two marking point commands (MRK₁,MRK₂) corresponds to a figure element (E₂) between two points (Q₁,Q₂), on the other curve (CV2), which include one (MRK₁) of said two marking point commands for one (Q₁) of the two points, and the other (MRK₂) of said two marking point commands for the other (Q₂) of the two points; a second step of partitioning the figure element (E₂) on the other curve (CV2) that corresponds to said point (P₁) on said one curve (CV1) by a predetermined partitioning number; and a third step of forming an edge surface portion (EG₁) by connecting said point (P₁) on the one curve (CV1) to all the partitioning points on the corresponding figure element (E₂) on the other curve (CV2). A method according to claim 1, characterised by having a step of inputting a partitioning pitch together with the definition statements defining the first and second curves (CV1,CV2), obtaining a partitioning number M of the longer (CV2) of the first and second curves in accordance with L/P, where P represents the partitioning pitch and L represents the length of the longer curve (CV2), and obtaining a partitioning number M j of a j-th figure element (E₂) of said longer curve (CV2) on the basis of (L j ·M/L), where L j represents the length of said figure element (E₂); wherein the partitioning number obtained is the predetermined partitioning number in said second step. A method according to claim 2, characterised by having a step of partitioning corresponding figure elements of the first and second curves by said partitioning number M j and establishing correspondence between figure element points on the first curve and figure element points on the second curve. A method according to any preceding claim characterised by machining the edge surface by moving a tool so as to traverse a point (P₁) on said one curve (CV1) at the same time as it traverses the or each corresponding point on the other curve (CV2).

Inventors: HOSONO, TAKESHI, SAMUKAWA, KOUJI, SEKI, MASAKI
Applicants: FANUC LTD.
Application year: 1987
Main classification: G05B19
IPC codes: G05B19