Closed-loop control system

DETAILED DESCRIPTION An apparatus and method for bending tubing, having a multiple number of bends uses a standard bending die.
As shown, a die that rotates while the tube is clamped in place is used.
The tube is guided with a wiper or pressure pad to reduce the tendency of the tube to flatten as the tube is bent around and against the outer periphery of the die.
The die has a drive that includes a sensor for measuring the bending moment necessary for making the desired bend, and controls use the bending moment as a parameter for automatically providing a desired overbend for that particular tube to compensate for springback when the die is released.
The drive or power element for rotating the bending die is controlled by a computer.
The bending moment being exerted is measured through the use of a force transducer or link and an encoder provides a signal indicating the amount of rotation of the die.
The die position signal and the load signal are used as inputs to determine the bending moment characteristics of the tube.
The information relating to the desired degree of bend is stored in the computer, and calculations are made online to determine the required number of degrees or angle of overbend for achieving the desired finished bend of that particular tube.
In addition, the amount of distortion of the tube during bending and its effect on springback can be programmed by empirical formulas into the computer.
Measured, historical and experimental information on the bending characteristics of tubing are used for providing compensation factors in the equations or formulas developed for determining the amount of overbend needed for each individual bend.
Analysis will show that the location of the neutral axis in any cross section of a homogeneous material coincides with the centroid of that cross section and thus the displacement of the neutral axis can also be calculated.
The ductility of the material will determine the minimum center line radius of the bend for any given tube, but in general, designing a bend to the largest practical radius makes the bend easier to form