BENDING ANGLE DETECTOR FOR USE IN A BENDING MACHINE

A bending angle detector for use in a bending machine, capable of detecting a bending angle of a workpiece with high accuracy even if workpieces of different materials are bent by the bending machine. The detector detects a bending angle in such a way that a coordinate transformation parameter is obtained from the image of each point of a virtual cubic lattice formed in space, the parameter being used for transformation between a space coordinate system in which each axis of the cubic lattice is set as a reference axis and a plane coordinate system which represents an image plane of the photographing means; a linear equation, which represents in the space coordinate system, each spot light projected on an outer face of the bent workpiece, is obtained; the space coordinates of three bright points, which are formed on the outer faces of the bent workpiece projecting three spot lights by three projectors, are obtained from the coordinate transformation parameter and the linear equation for each spot light, whereby a planar equation representing the three bright points is determined. The three spot lights may be replaced by two slit lights.