Springback angle measuring instrument for v-bending

Abstract

A springback angle measuring instrument for V-bending designed to detect the springback angle of a workpiece in such a way: A bending angle .theta..sub.1 of the workpiece is detected when an upper bender is lowered to an unloading starting position, and the instantaneous position of the upper bender and pressure imposed on the workpiece are detected while the upper bender being lifted at a very slow speed. The increment of the bending force per unit lifting distance of the upper bender is calculated and the bending angle of the workpiece at a point at which the increments of the bending force converge on a certain value is detected. Based on data on the bending angle and bending force obtained after this point, the relationship between the bending angle and the position of the upper bender and the relationship between the bending force and the position of the upper bender are respectively, approximated to a linear expression. The position of the upper bender where the bending force is zero is calculated from the linear approximate expression, and a bending angle .theta..sub.4 of the workpiece for this position is estimated. The bending angle .theta..sub. 1 for the unloading starting position is subtracted from the bending angle .theta..sub.4 to obtain the springback angle of the workpiece.