Image analysis – Applications – Manufacturing or product inspection
Patent
1994-08-31
1997-07-29
Boudreau, Leo
Image analysis
Applications
Manufacturing or product inspection
382152, 382258, G06K 900
Patent
active
056528051
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a bending angle detector for detecting a bending angle when a sheet-like workpiece is bent to a specified angle; a straight line extracting device for use with the bending angle detector; and a bending angle detecting position setting device for setting a detecting position when detecting a bending angle of a workpiece.
BACKGROUND OF THE INVENTION
There have been conventionally known the following bending angle detectors incorporated in bending machines such as press brakes.
(a) Contact type detectors which detect a bending angle of a workpiece, bringing a probe into contact with an inclined surface of the workpiece (e.g., Japanese Patent Publication Laid-Open No. 1-273618 (1989)).
(b) Non-contact type detectors which include a plurality of distance sensors such as overcurrent sensors, electrostatic capacity sensors or optical sensors and which detect a bending angle of a workpiece by measuring the difference between the distances from the respective distance sensors to the workpiece (e.g., Japanese Patent Publication Laid-Open No. 63-49327 (1988), Japanese Patent Publication Laid-Open No. 64-2723 (1989), Japanese Patent Publication Laid-Open No. 1-271013 (1989)).
These bending angle detectors however present the following drawbacks.
Firstly, the contact-type detectors cannot be suitably used when detecting a bending angle of a workpiece with short legs, as these detectors require comparatively long legs to ensure a high measuring accuracy. Further, if the contact type detectors are used for a long time, long contact with workpieces causes the probe to be worn and deformed, resulting in a decreased measuring accuracy.
In the case of the non-contact type detectors, a plurality of distance sensors are employed for measuring and calculating the distance from each sensor to a bent workpiece, but a long space cannot be kept between one sensor and another so that a satisfactory detecting accuracy cannot be obtained. Further, the non-contact type detectors employing overcurrent sensors or electrostatic capacity sensors have the disadvantage that since the outputs of these sensors vary depending on the material of a workpiece to be measured, so that measuring conditions have to be changed whenever a different material is used. The non-contact type detectors employing optical sensors also have the disadvantage that light directed to the surface of a workpiece disperses in some surface conditions, which leads to an increased measuring error and a decreased measuring accuracy. Another disadvantage of this type is that the measuring accuracy is dependent on sensors to be used and the resolving power of the image receptor.
One proposal to overcome the foregoing drawbacks is set out in Japanese Patent Publication Laid-Open No. 4-145315 (1992) where a slit light or two spot lights are directed onto the surface of a workpiece and a light image formed on the surface of the workpiece is photographed by a photographing means to detect a bending angle through image processing. In this bending angle detector, an optical system is arranged such that, as shown in FIG. 28, the optical axis of incident light upon the photographing means (i.e., camera) lies within a plane perpendicular to the irradiated surface of the workpiece W. In this arrangement, the following equations hold: light (or two spot lights) is directed onto the surface of the workpiece W; .theta.' is the angle formed by the slit light in an image plane; .theta. is a bending angle of the workpiece W (hereinafter referred to as "work angle"); and d, h, l respectively represent the lengths shown in FIG. 28.
From Equations (a), (b) and (c), the following equation (d) is obtained.
In Equation (d), since the beam projecting angle .alpha. is given, the work angle .theta. can be obtained by arithmetic operation if the angle .theta.'0 is detected by image processing.
As one example of the image processing technique, a device which linearizes image using the linear least square method is disclosed in Japanese Patent
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Ooenoki Toshiyuki
Otani Toshiro
Tokai Shigeru
Boudreau Leo
Kabushiki Kaisha Komatsu Seisakusho
Kelley Chris
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