JPH0821084B2 - Incomplete circle center detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an imperfect circular object (for example, an axis having a key groove, etc.) of a visual device applied as a robot eye for part handling or for measurement. ) Center detection method.

[Prior Art] It is important for measurement or robot handling to find the center (center of gravity when assuming that there is no incomplete part) of an incomplete circular object with some projections or chips on the visual device. Is. However, in the case of an incomplete circle, there is a large error if the center of gravity of the object is simply calculated like a circle. Therefore, when the incomplete portion is small and the position of the incomplete portion can be assumed in advance, the window can be applied while avoiding the incomplete portion and the center of the image can be obtained by processing the image in the window. Wish sho 61-50
499 "Method of detecting center of incomplete circle" and Japanese Patent Application No. 61-46238
"Circle center detection method"). These methods find the barycentric position or the average edge position of the image in the window, find the x-coordinate of the center from them, and then apply another window,
The y coordinate of the center is obtained by the same processing as described above.

[Problems to be Solved by the Invention] However, the conventional method described above cannot be applied when the incomplete portion as shown in FIG. 5 is large or when the position is indefinite.

An object of the present invention is to provide a method capable of obtaining the center of an incomplete circle even if the incomplete portion is large so as to occupy half of a circle or the position of the incomplete portion is indefinite.

[Means for Solving the Problems] The method for detecting the center of an incomplete circle according to the present invention is the length of an equivalent ellipse which is an ellipse in which the position of the center of gravity of an object and the moment of inertia about the object and the principal inertial axis and the minor inertial axis are equal. The length of the axis and the length of the minor axis are obtained, and a first straight line passing through the center of gravity and overlapping with the principal axis of inertia,
A second straight line passing through the center of gravity and forming an angle of π / 2 with respect to the first straight line; a third straight line passing through the center of gravity and forming an angle of π with respect to the first straight line; and the object Set an area of a predetermined size centered on the point where the distance from the center of gravity is (the length of the long axis + the length of the short axis) / 4 on each straight line at the intersections of the circumferential portions of Of the points in the area and on the circumference of the object, the points whose distance to the straight line is a fixed value or less are obtained, and the center of the circle passing through the three intersections is obtained.

[Operation] When the second straight line is set to the incomplete circle portion, there is no point on the circumference of the area and the distance to the straight line is equal to or less than the fixed value. At this time, if the second straight line is set again in the opposite direction of 180 °, the intersection point of the second straight line and the circumference of the object can be obtained. If three points on the circumference of the object are obtained as described above, the center of the circle passing through these three points becomes the center of the incomplete circle. As for the three points to be extracted, the accuracy of detecting the center of a circle passing through the three points can be secured if the arc angle formed by the two adjacent points is about 60 ° to 90 °, so a complete arc part can be about a half circle, and therefore, The size of the incomplete part can be about a half circle.

Example Next, an example of the present invention will be described with reference to the drawings.

1 to 4 are explanatory views of an embodiment of the method for detecting the center of an incomplete circle according to the present invention. FIG. 1 shows an equivalent ellipse 2 of an object 1, and FIG. 2 shows straight lines l ₁ and l. The intersection P _{K of 2} and l ₃ with object 1
P _L, illustrates the P _M, Figure 3 is the intersection point P _K, P _L, explanatory diagram of a method for obtaining the P _M, Figure 4 is a view showing a circle passing through three points P _K, P _L, the P _M is there.

In this embodiment, an incomplete circle 1 having an incomplete portion in the lower right part of the drawing as shown in FIG. 1 is targeted.

First, the image is taken in, the position of the center of gravity 3 of the object 1, the length Lmajor of the major axis 5 and the length of the minor axis 6 of the equivalent ellipse 2 (ellipse having the same inertia moment about the principal axis of inertia and the minor axis as the object 1) Lminor, the angle of principal axis of inertia θ (the angle formed by the long axis 5 and the x axis) is obtained (see FIG. 1).

Then, through the center of gravity 3, linear l ₁ slope of the principal axis of inertia angle theta, the street centroid 3, through a linear l ₂ and the center of gravity 3 inclination is θ + π / 2, the straight line l ₃ is inclination theta + [pi Intersection points P _K (x _K , y _K ), P _L (x _L , y _L ), P _M (x _M ,
y _M ) (see Fig. 2) is calculated point by point.

In this case, the points P _K , P _L , and P _M are calculated as follows.

As shown in FIG. 3, a point P (= P ₁ , P ₂ , P on the straight line l (= straight lines l ₁ , l ₂ , l ₃ ) where the distance dis from the center of gravity 3 is dis = (Lmajor + Lminor) / 4. ₃ ), and then a square area (11, 12, 13 in FIG. 2) whose one side is 2w (w = max (Lmajor-Lminor, const.)) Centered on the point P. Here, co
nst is a constant, Lmajor−Lminor when the imperfections are small
Is to set the minimum value in the above area.

Next, the point P _j (x _j , y _j ) on the circumference of the object 1 is extracted,
Check if the point is within the above area. If it is a point within the area, the distance r to the straight line 1 is calculated.
When the coordinates of the center of gravity 3 are (x _z , y _z ), the point P _j (x _j , y _j )
And the straight line l: ax + by + c = 0 (where a = -sinα, b = cos
α, c ＝ x _g sin α−y _g cos α) Becomes

If this distance r becomes equal to or less than Δ (constant), this point P _j is regarded as one point on the arc to be obtained, and this processing is ended. If it is larger than Δ or if the point P _j is outside the area, then the next point P _{j + 1} on the circumference
Is taken out and the above process is repeated.

When the straight line l ₂ is set toward the incomplete circle part, there is no point on the circumference of the square area and the distance r to the straight line l ₂ is Δ or less, but at this time, , Straight line l ₂ 180
° If set in the opposite direction, the intersection of the straight line l ₂ and the object 1 on the circumference can be obtained as described above.

When the three points P _K , P _L , and P _M are obtained as described above, the center of the circle passing through these three points P _K , P _L , and P _M becomes the center 4 of the incomplete circle 1.

The calculation formula at this time is, assuming that the coordinates of the center 4 to be obtained in FIG. 4 are (x _c , y _c ), However obtained as _{x LK = x L -x K x} MK = x M -x K y LK = y L -y K y MK = y M -y K.

When the position of the incomplete portion is known in advance, it takes time and effort to detect the position of the incomplete portion by extracting the target posture information (main axis of inertia and secondary axis) as in the present embodiment. That is, if the position of the incomplete portion is known in advance, draw a straight line that connects the incomplete portion and the center of gravity, set the intersection point of the arc on the opposite side of the incomplete portion and that straight line as P _L, and intersect the line at right angles. , 3 points on the circular arc can be obtained by setting the intersection points of the straight line passing through the center of gravity and the circular arc as P _M and P _K.

EFFECTS OF THE INVENTION As described above, the present invention avoids imperfections by using the principal axis of inertia of the object, extracts three points separated from each other on a complete arc, and determines the center of the circle passing through these three points. By calculating the center of an incomplete circle, the center can be correctly detected regardless of where the incomplete part is large and where the incomplete part is located. This has the effect of expanding the range of applications for visual devices in measurement and handling. There is.

[Brief description of drawings]

1 to 4 are explanatory views of an embodiment of the method for detecting an incomplete circle according to the present invention. FIG. 1 shows an equivalent ellipse 2 of an object 1, and FIG. 2 shows straight lines l ₁ and l _2. , the intersection of l ₃ and the target _{1 P K, P L, P} M
FIG. 3, FIG. 3 is an explanatory diagram of a method for obtaining the intersection points P _K , P _L , P _M , FIG. 4 is a diagram showing a circle passing through the three points P _K , P _L , P _M, and FIG. It is a figure which shows the example of the incomplete circle whose center is not calculated | required by the method of. 1 ... Target (incomplete circle), 2 ... Equivalent ellipse, 3 ... Center of gravity, 4 ... Center, 5 ... Long axis, 6 ... Short axis, 11, 12, 13 ...
… Square area.

Claims (1)

[Claims] 1. A method of detecting an incomplete circle center for an incomplete circular object partially lacking or protruding by using an image processing device to find the center of a perfect circle excluding the missing or protruding. Then, the position of the center of gravity of the object, the length of the major axis and the length of the minor axis of the equivalent ellipse, which is an ellipse having the same inertia moment about the principal axis of inertia and the minor axis of inertia as the object, are obtained, A first straight line overlapping the principal axis of inertia, a second straight line passing through the center of gravity and forming an angle of π / 2 with respect to the first straight line, passing through the center of gravity, and forming an angle of π with respect to the first straight line. The intersection of the third straight line and the circumference of the object is centered on each straight line at a distance of (the length of the major axis + the length of the minor axis) / 4 from the center of gravity. Area of a predetermined size to be set, among the points in the area on the circumference of the object, the distance to the straight line is A method for detecting the center of an incomplete circle, wherein the center of a circle passing through the three intersections is found by finding points below a certain value.