JP4253112B2 - Contour shape measuring method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention corrects a measurement point sequence at the center of a probe detected by a touch signal probe or the like used in a three-dimensional measuring machine by an amount corresponding to the tip radius of the probe in order to calculate the contour shape of the workpiece. The present invention relates to a contour shape measuring method and apparatus for measuring the contour shape of the above.
[0002]
[Prior art]
When measuring the contour shape of a workpiece using a touch signal probe of a coordinate measuring machine, etc., the probe is operated to bring a spherical probe tip into contact with the required location of the workpiece and obtain the required number of measurement point sequence data. Then, necessary measurement values are calculated from the measurement point sequence data. Since the measurement point sequence data is obtained as coordinate information of the center position of the probe tip, it is necessary to offset the measurement point sequence at the center of the probe tip by the probe radius in order to obtain the contour shape of the workpiece.
[0003]
As shown in FIG. 7, the conventional method for measuring the contour shape of a workpiece using the probe tip radius correction method is the number of neighbors of the measurement point sequence S1, S2,... Obtained as the center coordinates of the tip 10 of the probe whose tip radius is to be corrected. .. Is estimated from the point by some method, and the measurement points S1, S2,... Are moved in the direction by the tip radius r, thereby correcting the probe radius. Basically, the columns S1 ′, S2 ′,... Are obtained and used as measurement point sequences along the contour shape of the workpiece.
[0004]
[Problems to be solved by the invention]
However, in the probe tip radius correction method in the conventional contour shape measuring method described above, the estimated normal direction is the true direction due to a minute measurement error, for example, as shown by measurement points S13 and S14 in FIG. When the deviation is caused, the measurement point moves in such a shifted direction as the corrected measurement points S13 'and S14', so that the measurement error is enlarged according to the tip radius r, and the contour shape is increased. There is a problem that an incorrect measurement result such as crossing is obtained.
[0005]
The present invention has been made in view of such problems, and a contour shape measuring method capable of obtaining an appropriate contour shape even when a slight error occurs in the normal direction when correcting the probe tip radius, and An object is to provide an apparatus.
[0006]
[Means for Solving the Problems]
In the contour shape measuring method according to the present invention, the step of sampling the center position of the probe tip while bringing the probe tip into contact with the object to be measured to obtain the measurement point sequence, and the measurement point sequence obtained in this step, A step of generating an original contour by interpolating with a graphic element passing through a measurement point, a step of offsetting each graphic element constituting the original contour by a radius of the probe tip, and an offset graphic element obtained by offsetting the original contour On the other hand, an intersection between the offset graphic elements is obtained while tracking in a predetermined direction, and an offset contour is obtained by repeatedly moving to the offset graphic element existing on the side away from the original outline at the intersection obtained in this step. And a step.
[0007]
In addition, the contour shape measuring apparatus according to the present invention stores sampling means for sampling the center position of the probe tip that contacts the object to be measured, and a measurement point sequence of the center position of the probe tip sampled by the sampling means. Means for calculating an offset contour corrected by the radius of the probe tip from the measurement point sequence stored in the storage means as the contour shape of the measurement target, and the calculation means includes the storage means The original contour is generated by interpolating the measurement point sequence stored in the graph with the graphic elements that pass through each measurement point, and each graphic element constituting the original contour is offset by the radius of the probe tip, and the original contour is offset. The intersection of the offset graphic elements is obtained while tracking the offset graphic element in a predetermined direction. Characterized in that at the intersection obtained in step above and requests the offset contour while repeating to move to offset graphic elements present on the side away from the original outline.
[0008]
According to the present invention, when the offset contour is obtained, the original contour is generated by interpolating the measurement point sequence obtained as the center coordinates of the probe tip with the graphic element passing through each measurement point, and this original contour is formed. While offsetting each graphic element by the radius of the probe tip and tracking this offset graphic element in a predetermined direction, find the intersection of the offset graphic elements and exist on the side away from the original contour at the obtained intersection The offset contour is obtained while repeating the transition to the offset graphic element, so even if the offset contour intersects with some errors in the normal direction from the measurement point, By selecting an appropriate route at the intersection, an appropriate offset contour can be obtained.
[0009]
According to a preferred embodiment of the present invention, there is further provided a step of subdividing the obtained offset contour into a point sequence to obtain a measurement point sequence after the probe tip radius correction. Accordingly, a more appropriate contour shape can be obtained by interpolating between the newly obtained measurement point sequences with a smooth curve.
[0010]
In a further preferred embodiment of the present invention, the step of obtaining the offset contour includes, for example, a step of obtaining an intersection point of an nth (n = 1, 2,...) Graphic element and an (n + 1) th graphic element, and this step. When the intersection point is determined in step (i), the step of determining the nth graphic element with the point as the end point and the step of determining the intersection point do not determine the intersection point. Steps n-2,... are sequentially traced back to the previous graphic element, and when the intersection is found, the step of determining the njth graphic element is executed for all graphic elements while incrementing n. It is a step to do.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a contour shape measuring system according to an embodiment of the present invention.
The three-dimensional measuring machine 1 includes a table 3 on which a workpiece 2 as a measurement object is placed, a three-dimensional support mechanism 5 that supports the probe 4 movably in the XYZ axial directions, and the three-dimensional support. A contact-type probe 4 that is supported by the support mechanism 5 and contacts the workpiece 2 is provided. The probe 4 includes a spherical probe tip 10 at the tip, and outputs a contact signal by contacting the workpiece 2.
[0012]
Data of each measurement point obtained by moving the probe 4 of the coordinate measuring machine 1 along the outer shape of the workpiece 2 is sampled at a predetermined interval by the sampling unit 6. Data of each sampling point (measurement point sequence data) is temporarily stored in the memory unit 7. The calculation unit 8 reads the measurement point sequence data from the memory unit 7, performs probe tip radius correction, and calculates an offset contour graphic. The calculated offset contour graphic is displayed or printed out via the output unit 9 as necessary.
[0013]
Next, the operation of this system will be described. FIG. 2 explains the contour shape measurement processing by this system.
First, an original contour is generated by interpolating the measurement point sequence obtained as the center coordinates of the probe tip 10 with a line segment passing through each measurement point and an arc (S1). Next, an offset contour obtained by offsetting the original contour by the chip radius is obtained (S2). Finally, the offset contour is subdivided into a point sequence to obtain a point sequence after the probe tip radius correction (S3). FIG. 3A is an example of the original contour. When the offset contour is obtained by moving the measurement points S21, S22,... In the normal direction with respect to the original contour as in the prior art, the offset contour partially intersects as shown in FIG. However, in the present invention, the intersection of the offset graphic elements is obtained while tracking the offset graphic element obtained by offsetting the original contour in a predetermined direction. The offset contour is obtained while repeating the shift to the offset graphic element existing on the side away from the original contour. In other words, the contours are connected to achieve a consistent state. As a result of this processing, even if a part of the offset graphic elements intersects as shown in FIG. 8B, only the partial elements far from the original contour at the intersection S23 ″ are obtained as shown in FIG. Since it is selected and tracking moves, such an intersection will not occur.
[0014]
FIG. 4 is a flowchart for explaining a more specific processing procedure of the offset contour calculation processing (S2), and FIG. 5 is a diagram for explaining the specific processing.
First, an offset graphic element is generated by offsetting each line segment and arc constituting the original contour by a predetermined amount (probe tip radius r) (S11). In the case of the example of FIG. 5, if the center locus of the probe tip 10 is formed as A → B → C → D, the offset graphic elements for the contours A, B, C, and D are as follows: become.
[0015]
A → Line ▲ 1 ▼ and arc ▲ 2 ▼
B → Line ▲ 3 ▼
C → Line ▲ 4 ▼ and arc ▲ 5 ▼
D → Line ▲ 6 ▼
[0016]
In this example, each offset graphic element is always generated on the left side in the generation direction of the graphic elements A, B, C, and D constituting the original contour, as shown by an arrow in the figure, and a corner that is convex on the left side. A circular arc defined in the clockwise direction is inserted into the part. Each offset graphic element is traced in the same direction as the original contour for a straight line and traced clockwise for an arc. Note that this is a case where the workpiece 2 exists on the left side with respect to the original contour generation direction. If the workpiece 2 exists on the right side with respect to the original contour generation direction, the offset graphic element is the original contour. A counterclockwise circular arc is inserted into a corner portion that is generated on the right side with respect to the generation direction and is convex on the right side. While performing such tracking, the intersection of the nth offset graphic element and the (n + 1) th offset graphic element is obtained (S12). If there is an intersection (S13), the nth offset graphic is set with that point as the end point. The element is finalized (S14), and when there is no intersection (S13), the intersection is obtained by going back to the previous graphic element with n-1, n-2,. Is obtained, the njth graphic element is determined (S15). The above processing is executed for all offset graphic elements (S17).
[0017]
The above tracking process will be described as follows based on the example of FIG.
(1) Now, assuming that the starting point P of the offset graphic element {circle around (1)} is established, and tracing the offset graphic element {circle around (1)} in the tracking direction from P, the intersection point Q with the offset graphic element {circle around (2)} is obtained. Therefore, the offset graphic element (1) is determined.
(2) Next, when the offset graphic element {circle around (2)} is traced with Q as the starting point, the intersection R with the next offset element {circle around (3)} is obtained, and the offset graphic element {circle around (2)} is determined.
(3) Subsequently, when the offset graphic element (3) is traced with the starting point being R, in this case, since there is no intersection, the offset graphic element (3) is held and the offset graphic element (2) previously determined Returning ▼ to the uncertain element, the intersection of this graphic element (2) and the next graphic element (4) is obtained. As a result, the intersection point S between the graphic elements {circle around (2)} and {circle around (4)} is obtained, and the graphic element {circle around (2)} is determined again as an offset graphic element having the intersection point S as the end point.
[0018]
(4) Subsequently, when the offset graphic element (4) is traced with the start point as S, the intersection point T with the next offset graphic element (5) is obtained, so the graphic element (4) is determined with the intersection point T as the end point.
(5) Further, when the offset graphic element (5) is traced with the start point as T, the intersection point U with the next offset graphic element (6) is obtained, so the graphic element (5) is determined with the intersection point U as the end point.
Thereafter, the same processing is repeated. As a result, the determined offset graphic element becomes (1) (PQ) → (2) (QS) → (4) (ST) → (5) (TU) →... The shape portion is excluded, and an appropriate offset contour can be calculated.
[0019]
Whether or not the contour offset figure has an arc element at the corner is determined by whether or not the corner of the original contour is convex in the offset direction, which is to obtain a two-element outer product vector that generates a corner. The determination may be made with the sign. That is, if the outer product vector is positive, it can be determined that the corner is bent to the left with respect to the tracking direction, and if the outer product vector is negative, it can be determined that the corner is bent to the right with respect to the tracking direction. At this time, if the contour element is a circular arc, the determination is made by replacing it with the connection at the intersection of the two elements. When the contour tracking direction is different between the original contour and the offset contour, all the tracking directions described above may be reversed.
[0020]
In the above embodiment, the method of inserting an arc is used as an interpolation method for the convex corner portion of the original contour. However, in addition to the insertion of the arc shown in FIG. 6A, as shown in FIG. Extend the two elements that form the corner to the intersection, or extend the two elements that form the corner in the direction of the intersection and insert an arc as shown in FIG. Also good.
[0021]
【The invention's effect】
As described above, according to the present invention, when the offset contour is obtained, the original contour is generated by interpolating the measurement point sequence obtained as the center coordinates of the probe tip with the graphic element passing through each measurement point. While offsetting each figure element composing the original outline by the radius of the probe tip, tracing the offset figure element in a predetermined direction, the intersection of the offset figure elements is obtained, and the original outline at the obtained intersection point Since the offset contour is obtained while repeating the transition to the offset graphic element that exists on the side away from the case, there is a slight error in the normal direction from the measurement point, and the offset contour intersects However, an appropriate offset contour can be obtained by selecting an appropriate route at the intersection of the offset contours.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a contour shape measuring system according to an embodiment of the present invention.
FIG. 2 is a flowchart of the contour shape measurement process.
FIG. 3 is a diagram for explaining the contour shape measurement process;
FIG. 4 is a flowchart showing an offset contour generation process in the contour shape measurement process.
FIG. 5 is a diagram for explaining a specific example of the offset contour generation processing;
FIG. 6 is a diagram for explaining a corner processing method when generating the offset contour.
FIG. 7 is a diagram for explaining a conventional general probe tip radius correction process;
FIG. 8 is a diagram for explaining a problem in the conventional probe tip radius correction process.
[Explanation of symbols]
1 ... coordinate measuring machine, 2 ... workpiece, 3 ... table, 4 ... probe, 5 ... three-dimensional support mechanism, 6 ... 2 _1, 2 ₂ ... camera, 3 ... image memory, 4 ... processing unit, 5 ... work Memory, 6 ... Sampling unit, 7 ... Memory unit, 8 ... Calculation unit, 9 ... Output unit, 10 ... Probe tip.

Claims (3)

Sampling the center position of the probe tip while bringing the probe tip into contact with the object to be measured to obtain a measurement point sequence;
Interpolating the measurement point sequence acquired in this step with a graphic element passing through each measurement point, and generating an original contour;
A step that generates an offset graphic elements each graphic element constituting the original contour by offset radius of the probe tip,
a step of obtaining an intersection of an nth (n = 1, 2,...) offset graphic element and an (n + 1) th offset graphic element, and when an intersection is obtained in this step, the nth graphic element is determined using that point as an end point. When the intersection point is not obtained in the step of determining and the step of obtaining the intersection point, the intersection point is traced back to the previous offset graphic element in order of n−1, n−2,. Obtaining the offset contour by executing the step of determining the nj-th offset graphic element at the time when the intersection is obtained, by executing the step for all offset graphic elements while incrementing n ;
A contour shape measuring method comprising:   2. The contour shape measuring method according to claim 1, further comprising a step of subdividing the obtained offset contour into a point sequence to obtain a measurement point sequence after correcting the probe tip radius. Sampling means for sampling the center position of the probe tip that contacts the object to be measured;
Storage means for storing a measurement point sequence of the center position of the probe tip sampled by the sampling means;
Calculating means for obtaining, as the contour shape of the object to be measured, an offset contour corrected by the radius of the probe tip from the measurement point sequence stored in the storage means,
The computing means is
The measurement point sequence stored in the storage means is interpolated with graphic elements passing through the respective measurement points to generate original contours, and each graphic element constituting the original contours is offset by the radius of the probe tip to create an offset graphic. An element is generated, and for every offset graphic element while incrementing n, the intersection of the nth (n = 1, 2,...) Offset graphic element and the (n + 1) th offset graphic element is obtained, and the intersection is obtained. The nth graphic element is determined with the point as the end point, and when the intersection cannot be obtained, the n + 1, n-2,... A contour characterized in that the offset contour is obtained by repeating the process of determining the intersection point retrospectively and determining the nj-th offset graphic element when the intersection is determined. Shape measuring device.

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