PROFILING METHOD

Abstract: A limit is set to one axis of a tracer head (TC) and limits set, one being parallel and the other orthogonal to the direction of movement inside a moving plane determined by the limit. A polarity judgement device sets the polarity of the limit set in the direction of the movement of the tracer head (TC). A clamp limits profiling, within a range defined by the set limits.

Description: The present invention relates to a contour profiling method for the execution of machining in which the outer part or inner part of a workpiece is cut away along the contour of a model. In machining a workpiece, the workpiece generally is rough-machined into a desired shape and thereafter is subjected to finishing machining. In particular, when a metal mold is machined from a solid material (workpiece), the process of rough machining is often given much weight. Though automation, namely the implementation of numerical control (NC), is making progress with regard to the machining of metal molds, an improvement in the efficiency of rough machining processes is especially required. Heretofore, in the rough machining of pockets or the like, milling in 2 1/2 dimensions has been carried out in such a manner that, as shown in Fig. 10(A), a cutter 2 is moved in an X-Y plane at a height Z₁ so as to cut away a designated area AR1 of a workpiece 1, whereupon the cutter 2 is lowered to a height Z₂ so as to cut away areas AR2 and AR3 of the workpiece 1 at this height, as shown in Fig. 10(B). With rough machining based on such conventional milling, however, a problem encountered is that a long period of time is required, thereby diminishing machining efficiency. Particularly in the machining of metal molds, apart from the long period of time expended on rough machining, smoothening of the machined surface to the greatest extent possible is demanded in order to raise the efficiency of finish machining which follows the rough machining. The present invention has been devised in order to solve these problems, and its object is to provide a contour profiling method which shortens the period of time for rough machining and which in a development may form a smooth machined surface. EP-A-0036458 discloses a contour profiling method according to the preamble of the attached claim 1, wherein a clamping function is applied in the Z-axis direction, and EP-A-0034006 discloses a similar contour profiling method wherein limits of a tracing path are set around the shape of a tracing model, and no clamping function is employed. According to the present invention there is provided a contour profiling method wherein a tracer head and a model are moved relative to one another in the directions of three axes to trace the shape of the model, and the amount of movement of a cutting tool relative to a workpiece is controlled in synchronism with the relative tracing displacement of the tracer head, the relative movement of the tracer head in the direction of one of said axes being limited to set successive stop points along this axis thereby to set a plurality of tracing planes orthogonal to said axis and in which model tracing is executed, this tracing being executed with a clamping function being applied, characterised in that in each of said plurality of tracing planes the tracer head moves relative to the model in the direction of one axis along paths limited in positive and negative directions, and also in the direction of an orthogonal axis along paths limited in positive and negative directions, the tracer head moving relative to the model in the directions of said one axis and said orthogonal axis alternately in either a converging or diverging manner, thereby to trace around a convex or a concave contour respectively of the model in that particular tracing plane, with the clamping function being applied in the tracing plane. Thus, with a contour profiling method of the present invention, the operation of the cutting tool is controlled in synchronization with the tracer head movable in the directions of the three axes along the model shape, and in both cases where the model shape is concave and convex, rough machining can be performed with contour profiling clamped, in a range defined by the set limits. In a development, machining based on contour profiling equivalent to that of finish machining can be performed with the clamp released. Therefore, a smooth machined surface can be formed efficiently, at the same time as rough machining, by utilizing the contour profiling function. Brief Description of the Drawings Figs. 1 through 8 are diagrams for explaining tracing operations according to the present invention; Fig. 9 is an explanatory structural view showing an example of a contour profiling machine for carrying out the present invention; and Figs. 10(A) and (B) are explanatory views showing an example of rough machining in the prior art. Examples of the present invention will now be described in detail with reference to the drawings. Fig. 9 is an explanatory view of a machine for carrying out the present invention. A contour profiling machine TDM has a tracer head TC and a cutter CT. The tracer head TC has a stylus 4 at its distal end, the stylus 4 is held so as to be finely movable along a Z axis, an X axis and a Y axis, and the fine movement of the stylus 4 is detected and outputted as a displacement magnitude ε by a differential detector. The cutter CT is, for example, a cutting tool 5. MDL denotes a model as stated before, and WK a workpiece 1 as stated before. CLM indicates a column on which the tracer head TC and the cutter CT are installed, and ZM a Z-axis motor which drives and feeds the column CLM along the Z axis. Shown at TBL is a table on which the model MDL and the workpiece WK are placed, and which is movable in the X and Y directions. XM and YM indicate X-axis and Y-axis motors which drive and feed the table TBL along the X axis and Y axis, respectively. The contour profiling machine TDM is constructed of these components. SVX, SVY and SVZ represent X-, Y- and Z-axis servo circuits, respectively, and symbol NC represents a tracing numerical controller. PC denotes the processor of the tracing numerical controller for executing ordinary tracing calculations, and MEM the meory of the tracing numerical controller for storing programs, data, etc. Next, tracing operations in the contour profiling machine TDM will be described. In the present invention, the machine is controlled so as to perform a converging-type operation in case of a convex model shape and to perform a diverging-type operation in case of a concave model shape. Fig. 1(A) shows the side shape of the model, and stop points as to the Z axis are first set here. This serves to set a plurality of X-Y planes through the repeating function of the contour profiling machine. A starting point shall be determined on an X-Y plane which is limited by stop points as shown in Fig. 1(B) by way of example. If the start point determined does not lie on or in the model MDL, the Z axis is clamped and the tracer head is moved a traveling distance a based on an "initial movement quantity a" designated according to the setting of a "tracing direction". Any ±X and ±Y from the starting point can be selected as the "tracing direction", and the "initial movement quantity a" is set as an incremental quantity having no sign. The tracer head has the polarity of a limit set in the direction of movement thus stipulated by the "tracing direction", and is moved to point A in a state where contour profiling is clamped within a range defined by the set limit. Here the tracer head does not come into contact with the model before reaching the point A. At the point A, instead of the limit used thus far, a new limit orthogonal thereto is set. With regard to the direction of rotation at point A, the counter-clockwise direction is designated by the sign "+" and the clockwise direction by the sign "-", as illustrated in Fig. 2. Here, the "direction of rotation" is designated as "-", and a distance b is designated as a second "initial movement quantity b". At the point B, a new limit is set clockwise just as at the point A, and a value with a "depth of cut d" added to the distance a is designated as a movement quantity. As a result, in setting a new limit at a point C again, the tracer head draws somewhat closer to the model. In this manner, the tracer head is successively moved to points D, E, F ... with contour profiling clamped, and the head comes into contact with the surface of the model, in a direction of movement stipulated by a limit, at a point H. When the tracer head thus contacts the model while moving with contour profiling clamped, the clamped state is released and contour profiling along the shape of the model is carried out. If the tracer head is still in contact with the model even in a case where the traveling distance along the X axis has exceeded a predetermined distance stipulated by the point H as shown in the drawing, then the unclamped state is maintained and contour profiling along the model shape is performed continuously. The above operations are repeated until the following condition holds: The tracer head makes one revolution around the model owing to resetting of the limits four times, and movement of the tracer head is ended in a case where the stylus of the tracer head has been constantly in contact with either the model or an end limit to be described later, during the revolution, or in a case where the value of either traveling distance a or b updated by the "depth of cut" d has become negative. Fig. 3 shows an example of movement planes determined when specified Z-axis stop points have been set in a model having the same side shape as in Fig. 1(A). In this case, when contour profiling which merely converges toward the center of the model as in Fig. 1(B) is performed, the central hatched part of the model shape which is hollow is left uncut. In Fig. 4, in order to prevent such an uncut part, a "target point" M is set and limits are set so that the end point of the movement of the tracer head will approach the "target point." In setting the point, a condition is that half-lines along the X and Y axes with this point as the origin do not intersect the contour of the model two or more times. Fig. 5 shows an example of the diverging-type clamped tracing performed in case of a concave model. With regard to the direction of rotation from a starting point, the counter-clockwise direction is designated by + and the clockwise direction by -, as illustrated in Fig. 6. The diverging-type clamped tracing differs from the above-stated converging-type in the sign of the depth of cut d and an end condition. As to the setting of the starting point, a condition is that half-lines along the X and Y axes with this point as the origin do not intersect the contour of the model two or more time, just as set forth concerning the end point of the diverging-type clamped tracing. Regarding the traveling speed of the cutting tool, a deceleration area is set at a part e in each path, as illustrated in Figs. 7(A) and (B). That is, when a remaining amount on one path has become less than a value set in a specified system parameter (#7941), the traveling speed is changed to a speed set in another system parameter (#7942). However, when a command speed is equal to or lower than the speed stipulated by the system parameter, the speed does not change. Fig. 8 illustrates a method of setting end limits in the case of the diverging-type clamped tracing. In the case of the diverging type, areas to be machined can be designated by setting the limits of ±X and ±Y. In the illustrated example, machining with movement along the Y axis in the negative direction beyond -Y is forbidden. Though various specific examples of the present invention have been described, the invention is not limited thereto but can be modified in a variety of ways without departing from the scope of the claims. The contour profiling method of the present invention can perform rough machining with contour profiling clamped, within a range defined by set limits, in cases where the shape of a model is concave and convex, and the method is capable of forming a smooth machined surface efficiently by utilizing the contour profiling function.

Claims: A contour profiling method wherein a tracer head (TC) and a model (MDL) are moved relative to one another in the directions of three axes (X, Y, Z) to trace the shape of the model (MDL), and the amount of movement of a cutting tool (5) relative to a workpiece (WK) is controlled in synchronism with the relative tracing displacement of the tracer head (TC), the relative movement of the tracer head (TC) in the direction of one of said axes (Z) being limited to set successive stop points along this axis (Z) thereby to set a plurality of tracing planes (X-Y) orthogonal to said axis (Z) and in which model tracing is executed, this tracing being executed with a clamping function being applied, characterised in that in each of said plurality of tracing planes (X-Y) the tracer head (TC) moves relative to the model (MDL) in the direction of one axis (X) along paths limited in positive and negative directions, and also in the direction of an orthogonal axis (Y) along paths limited in positive and negative directions, the tracer head moving relative to the model (MDL) in the directions of said one axis (X) and said orthogonal axis (Y) alternately in either a converging or diverging manner, thereby to trace around a convex or a concave contour respectively of the model (MDL) in that particular tracing plane, with the clamping function being applied in the tracing plane. A contour profiling method according to claim 1, wherein the clamping function is released when said tracer head (TC) contacts the model (MDL) while moving with contour profiling clamped. A contour profiling method according to claim 2, wherein it is detected whether or not said tracer head (TC) is still in contact with said model (MDL) when it has moved a predetermined relative distance, and an unclamped state is maintained if the said tracer head (TC) and said model (MDL) are thereby detected to be still in contact. A contour profiling method according to any preceding claim, wherein after said tracer head (TC) has moved relative to the model (MDL) a predetermined distance (a,b) in the direction of an axis (X,Y) along a tracing plane (X-Y), a new limit is formed which is orthogonal to the preceding limit within the tracing plane (X-Y). A contour profiling method according to claim 4 when appended to claim 2 or 3, comprising discriminating whether or not the new formed limit lies inside the model (MDL), and an unclamped state is maintained irrespective of a new set limit when the new limit has been discriminated to lie inside the model (MDL). A contour profiling method according to claim 4 or 5, wherein travelling distances are stored so that the new limits to be set within the tracing plane (X-Y) will change in predetermined constant value increments.

Inventors: MATSUURA HITOSHI, TSUKAMOTO OSAMU FANUC MANSION, MATSUURA, HITOSHI, TSUKAMOTO, OSAMU FANUC MANSION HARIMOMI 6-105
Applicants: FANUC LTD, FANUC LTD.
Application year: 1988
Main classification: B23Q35
IPC codes: B23Q35, B23Q33