JP4944081B2 - Judgment method of mesh data - Google Patents

Description

  The present invention relates to a mesh data determination method for specifying a noise portion of mesh data by a computer after measuring a surface shape of a workpiece with a measuring instrument to obtain mesh data including a plurality of mesh elements.

  Conventionally, when manufacturing a mold for press molding, a mold is designed by using CAD or the like from shape data of a molded product, and mold data is generated. NC machining data for machining a mold is created based on the obtained mold data, and the mold as the first stage is machined using an NC machine tool. The mold at this stage is not always capable of molding a desired product, but verification is performed based on a molded product actually obtained through trial use, and a skilled technician can correct the mold. Generally done.

  Recently, in order to mass-produce products, it is desired to prepare a plurality of the same molds and press-mold each, and the mold obtained by modification is the first mold, and the first mold A corresponding second type (or repeat type) is created. In order to create the second type, it is desirable to efficiently suppress the correction process performed by the skilled technician performed by the first type as much as possible.

  For this reason, in Patent Document 1, the obtained first mold is measured with a three-dimensional measuring device, a curved surface is created from the obtained three-dimensional point cloud data, and NC machining data for shape machining is obtained based on the curved surface data. It has been proposed to create. Data obtained by measurement with a three-dimensional measuring device may be represented by mesh data as described in Patent Document 2.

  By the way, in the first mold obtained by the correction, there may be a noise such as a nest appearing as a result of the correction, a screw hole for mounting a component, a scratch or a step generated for a predetermined reason. Such noise should not be reflected in the shape surface data to be three-dimensionally processed. When the first type is measured with a three-dimensional measuring instrument as in Cited Document 1, since such noise is also measured, the computer operator specifies the location of the noise from the mesh data in the subsequent process. It is necessary to perform a predetermined correction process.

  Patent Document 2 describes that a candidate mesh and a mapping model satisfying a mesh evaluation criterion are displayed on a screen, and an operator selects a desired mesh.

JP 2006-320996 A JP-A-11-96398

  The amount of mesh data obtained by measuring the first mold with a three-dimensional measuring instrument is large, and it is burdensome for the operator to specify the noise part. Requires skill.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a mesh data determination method that can easily and reliably specify a noise portion from mesh data.

  The mesh data determining method according to the present invention is a mesh for specifying a noise portion of the mesh data by a computer after measuring the surface shape of the workpiece with a measuring instrument to obtain mesh data composed of a plurality of mesh elements. In the data determination method, a first step of identifying a predetermined reference node from the mesh data, and all adjacent nodes adjacent to the reference node via one side of the mesh element, and for all the adjacent nodes A second step of obtaining an average surface; a third step of obtaining a separation distance between the average surface and the reference node; and when the separation distance is smaller than a predetermined threshold, the reference node is set as a normal node, and the separation distance is And a fourth step of setting the reference node as a noise node when the threshold is equal to or greater than the predetermined threshold value.

  As described above, if the reference node is specified as a noise node when the distance between the average plane and the reference node is equal to or greater than a predetermined threshold, the computer can automatically and easily specify the noise portion.

  When the average surface is obtained by the least square method based on all the adjacent nodes, the average surface is appropriately obtained.

  After the fourth step, all mesh elements around the noise node may be specified as noise elements. Thereby, the operator can easily recognize the result of the noise determination.

  According to the method for determining mesh data according to the present invention, when the distance between the average plane obtained from a plurality of adjacent nodes and the reference node is equal to or greater than a predetermined threshold, the reference node is automatically identified as a noise node. Therefore, the noise part can be specified easily and reliably.

  Hereinafter, the mesh data determination method according to the present invention will be described with reference to FIGS.

  First, a schematic procedure will be described with respect to a pre-process for processing of the mesh data determination method according to the present embodiment.

  In step S1 of FIG. 1, the molded product to be obtained is designed, and data of the molded product model is created.

  In step S2, mold model data data is created by CAD based on the molded product model data.

  In step S3, NC machining data for the NC machine tool is created based on the data of the mold model data.

  In step S4, a mold is formed by the NC machine tool using the obtained NC machining data.

  In step S5, press working is performed using a mold molded as a tryout to obtain a molded product as a prototype.

  In step S6, the prototype and the die press surface are observed and examined, and the die is corrected manually. At this time, the prototype is observed and examined for wrinkles and cracks, dimensional errors, etc., and the mold is corrected by comprehensively considering the condition of the surface of the press. Steps S5 and S6 may be repeated several times.

  In this step S6, there is a case where a nest appears on the surface due to the correction to the mold, or a scratch or a step is generated for some reason. Further, depending on the design conditions, a screw hole for mounting components may be provided on the mold. These nests, scratches, steps, holes and the like should not be reflected in the shape surface data to be three-dimensionally processed.

  In step S7, the surface shape of the mold (work) corrected by a non-contact optical three-dimensional measuring instrument or the like is measured three-dimensionally to obtain three-dimensional measurement data composed of point groups. As a means for measuring the surface shape of the mold, another measuring device such as a contact type may be used.

  In this step S7, nests, scratches, steps, holes and the like existing in the mold are also measured, and this becomes a noise portion that should not be reflected in the shape surface data on the data.

  In step S8, the point group of the three-dimensional measurement data is set to a large number of triangular polygons (mesh elements) by a predetermined means using a computer to obtain mesh data. These triangular polygons indicate the measured mold surface shape. The mesh data obtained in step S8 includes the noise part as it is. FIG. 2 shows mesh data 10 as an example. The mesh data 10 is composed of a large number of triangular polygons 12 and represents the surface shape of the mold, and adjacent polygons 12 share one side of the same length. A triangular vertex of the polygon 12 is a node 14.

  After such a pre-process, the mesh data determination method according to the present embodiment for specifying a noise portion is performed. First, the basic concept of the mesh data determination method will be described on a two-dimensional plane.

  As shown in FIG. 3, when a plurality of nodes 14 are represented on the same plane, a predetermined node 14 is selected as a reference node 14a, and two nodes 14 adjacent to the reference node 14a are selected as adjacent nodes 14b. To do. A circle 16 having a radius r in contact with the reference node 14a and two adjacent nodes 14b and a reference line 18 connecting the two adjacent nodes 14b are defined.

  When machining a die based on the mesh data 10, the tool of the machine tool does not machine along the surface of the polygon 12, but works along a curve that smoothly connects the nodes 14 to each other. Therefore, the circle 16 is substantially equal to the movement path of the tool.

  Focusing on the left adjacent node 14b (hereinafter, referred to as the adjacent node 14c), the angle between the adjacent node 14c and the reference node 14a with respect to the center point O of the circle 16 is defined as θ. A straight line 22 passing through the midpoint 20 and the center point O between the adjacent node 14c and the reference node 14a is defined, and the distance between the circle 16 and the midpoint 20 on the straight line 22 is a shape tolerance t. The shape tolerance t is desirably as small as possible because it indicates the distance between the tool movement path and the polygon 12, but it is not reasonable to make it excessively smaller than the machining accuracy of the machine tool. Therefore, the shape tolerance t is set to a reasonably small value based on the machining accuracy of the machine tool.

  In the right triangle formed by the adjacent node 14c, the midpoint 20 and the center point O, the adjacent node 14c to the midpoint 20 is x, and the midpoint 20 to the center point O is y. In the reference line 18, z is defined as the distance between the intersection with the perpendicular 24 drawn from the reference node 14 a and the adjacent node 14 c. An isosceles angle of an isosceles triangle formed by the reference node 14a, the adjacent node 14c, and the center point O is α. The length MT of the perpendicular 24 (hereinafter referred to as threshold value MT) is obtained by the following calculation.

x = r × sin (θ / 2)
z = r × sin θ
t = x × tan (θ / 4)
MT = z × tan (θ / 2)
Putting these equations together,
MT = t × 4
The threshold value MT can be defined as four times the shape tolerance t.

  By the way, since the mesh data 10 is originally obtained by measuring the first mold, the shape tolerance t does not become excessively large in theory, but it is actually a portion where it increases. There is. This can be determined to be noise caused by the target reference node 14a due to a nest, a flaw, a step, a hole or the like existing in the mold.

  Based on such a concept, when the noise portion of the mesh data 10 is specified, since the mesh data 10 is a set of data of the node 14 without surface data, the shape tolerance t is directly obtained. Therefore, it is desirable to make a noise determination with a threshold based on the shape tolerance arbitrarily defined by the threshold MT of the perpendicular 24. In the determination based on the threshold MT, a plurality of polygons 12 existing around the reference node 14a can be determined collectively. FIG. 3 is a diagram for explaining the relationship between the shape tolerance t and the threshold value MT. Although the threshold value MT is a fixed value, the length d of the perpendicular 24 varies.

  Next, processing of the mesh data determination method according to the present embodiment will be described with reference to FIG. The processing shown in FIG. 4 is basically automatically performed by computer program processing, but it is not necessary to perform all the steps by one computer. For example, the display processing in step S110 is performed by a display-only computer. You may go. Further, part or all of the noise removal processing in step S111 may be performed manually.

  In step S101 of FIG. 4, as shown in FIG. 5, one reference node 14a as an evaluation target point is selected from all the nodes 14 included in the mesh data 10. This step S101 is included in a series of loop processes described below, and selects one of the unprocessed nodes 14 as the reference node 14a.

  In step S102, all adjacent nodes 14b adjacent to the reference node 14a through one side of the polygon 12 (that is, one ball node) are specified. In the example shown in FIG. 5, there are seven polygons 12 around the reference node 14a and seven adjacent nodes 14b. The number of adjacent nodes 14b with respect to the predetermined reference node 14a is 3 or more.

  In step S103, as shown in FIG. 6, the average plane 30 is obtained by the least square method based on all the obtained adjacent nodes 14b. According to the method of least squares, the average plane 30 is appropriately obtained, and the subsequent processing becomes simple. The average surface 30 corresponds to the reference line 18 in FIG. In the least square method for obtaining the average plane 30, the reference node 14a need not be included. The reference node 14 a may exist on the upper side of the average surface 30, may exist on the lower side, and may exist on the average surface 30.

  The average surface 30 is basically a plane, but may be approximated to a curved surface depending on design conditions.

  In step S104, as shown in FIG. 7, the reference node 14a is projected onto the average plane 30, and the perpendicular line 24 is set.

  In step S105, a separation distance d between the projection point of the reference node 14a with respect to the average plane 30 and the reference node 14a (that is, the length of the perpendicular 24) is obtained. The separation distance d may be obtained in the same manner regardless of whether the reference node 14a is on the upper side or the lower side of the average plane 30.

  In step S106, the separation distance d is compared with the threshold value MT. If d <MT, the process proceeds to step S107, and if d ≧ MT, the process proceeds to step S108. Here, the threshold value MT is MT = 4 × t as described above, but the value may be slightly increased or decreased depending on design conditions.

  In step S107, the current reference node 14a is recorded as a normal node.

  In step S108, the current reference node 14a is recorded as a noise node.

  After steps S107 and S108, it is confirmed in step S109 whether all the nodes 14 included in the mesh data 10 have been subjected to the determination process as the reference node 14a. If the processing has been completed for all the nodes 14, the process proceeds to step S110, and if any of the nodes 14 has not been processed, the process returns to step S101.

  Basically, the above-described determination process is performed for all the nodes 14, but depending on the design conditions, the determination process for the nodes 14 in a predetermined range may be omitted for efficiency.

  In step S110, as shown in FIG. 8, all polygons 12 around the node 14 recorded as the noise node 32 are specified as noise polygons (noise elements) 34. In other words, the polygon 12 in which at least one of the three nodes 14 is specified as the noise node 32 may be specified as the noise polygon 34.

  The noise polygon 34 is displayed on the computer monitor screen 38 in a color different from that of the normal polygon 12. Thereby, the operator can easily recognize the result of the noise determination. As is apparent from FIG. 8, a certain range can be specified as the noise portion. In FIG. 8 (and FIG. 9), the noise node 32 is indicated by a white circle, and the noise polygon 34 is hatched.

  In step S111, a predetermined smoothing process or the like is performed on the part specified as the noise part to remove the noise. Thereby, the process shown in FIG. 4 is completed, and according to the obtained mesh data 10, it is possible to create high-precision mold machining data without noise traces.

  The inventor applied and tried the mesh data determination method according to the present embodiment to a sample work having a low linear step. A plan view of the resulting mesh data 10 is shown in FIG. In FIG. 9, the hatched portion is a noise polygon 34, and the vertical line 36 is a step. It will be understood that the noise polygon 34 is clearly along the vertical line 36 of the step and occupies a moderate width that can be easily recognized. It will also be understood that the mesh data determination method according to the present embodiment is particularly effective against continuous noise such as the vertical line 36.

  The inventor examined several determination methods in addition to the mesh data determination method according to the present embodiment. One of them is a determination process based on the magnitude of the angle θ formed by the two polygons 12 in FIG. That is, when the angle θ is excessive, the polygons 12 on both sides can be determined as noise polygons 34.

  FIG. 10 shows the result of applying the determination method according to this alternative for the same work as in FIG. In this case, since the determination process is performed based on the side shared by the two polygons 12, only the two polygons are determined as the noise polygon 34 by one determination process, and it is difficult to form a collective shape. . Compared with FIG. 9, the vertical line 36 is not easily recognized, and the effectiveness of the mesh data determination method according to the present embodiment will be understood. The determination process shown in FIG. 10 is also effective for specific applications such as determination of small and discontinuous noise.

  As described above, according to the mesh data determination method according to the present embodiment, when the distance d between the average surface 30 and the reference node 14a is equal to or greater than the threshold value MT, all the polygons 12 including the reference node 14a are obtained. By specifying as a noise polygon, it is possible to automatically and reliably specify a noise portion using a computer.

  Further, as shown in FIG. 4, for one reference node 14a, the basic points include identification of the adjacent node 14b, calculation of the average plane 30, calculation of the separation distance d, separation distance d and threshold MT. The determination process is performed only by comparing the two, the process is simple, and the load on the computer is small.

  The mesh elements constituting the mesh data 10 are triangular polygons 12, which are easier to process than polygons such as quadrangular shapes.

  Although the data amount of the mesh data 10 is large, in the mesh data determination method according to the present embodiment, the noise portion is basically specified by a computer, and the burden on the operator is small. Learning is easy.

  The mesh data determination method according to the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

It is a flowchart which shows the procedure of the pre-process of the determination method of the mesh data which concerns on this Embodiment. Mesh data. It is explanatory drawing which shows the concept of the determination method of mesh data on a two-dimensional surface. It is a flowchart which shows the procedure of the determination method of the mesh data which concerns on this Embodiment. It is a top view which shows a reference | standard node and an adjacent node in a part of mesh data. It is a perspective view which shows a reference node, an adjacent node, and an average surface in a part of mesh data. It is the schematic diagram which projected the reference node, the adjacent node, and the average surface in the horizontal direction in a part of mesh data. This is mesh data in which a noise polygon is specified. It is a top view of the mesh data as a result of trying the determination method of mesh data concerning this embodiment to predetermined work. It is a top view of the mesh data as a result of trying the determination method of the mesh data concerning another plan to a predetermined work.

Explanation of symbols

10 ... Mesh data 12 ... Polygon (mesh element)
14 ... Node 14a ... Reference nodes 14b, 14c ... Adjacent node 24 ... Vertical line 30 ... Average surface 32 ... Noise node 34 ... Noise polygon (noise element) MT ... Threshold d ... Separation distance t ... Shape tolerance

Claims (3)

In the determination method of mesh data for specifying the noise part of the mesh data by a computer after measuring the surface shape of the workpiece with a measuring instrument and obtaining mesh data composed of a plurality of mesh elements,
A first step of identifying a predetermined reference node from the mesh data and all adjacent nodes adjacent to the reference node via one side of the mesh element;
A second step of determining an average plane for all the adjacent nodes;
A third step of obtaining a separation distance between the average surface and the reference node;
A fourth step of setting the reference node as a normal node when the separation distance is smaller than a predetermined threshold, and setting the reference node as a noise node when the separation distance is equal to or greater than the predetermined threshold;
A method for determining mesh data, comprising: The method for determining mesh data according to claim 1,
The method of determining mesh data, wherein the average surface is obtained by a least square method based on all the adjacent nodes. In the determination method of the mesh data according to claim 1 or 2,
After the fourth step, all the mesh elements around the noise node are specified as noise elements.

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