Title:	REAL-TIME STEREO COMPUTATION IN SHEET HYDROFORMING PROCESSES
Author(s):	A. Izaguirreb , N. Aranab , J. Barbariasb , C. Garcíaa , A. Aginagaldea , J.a. Esnaolaa
ISBN:	972-8924-09-7
Editors:	Nuno Guimarães, Pedro Isaías and Ambrosio Goikoetxea
Year:	2006
Edition:	Single
Keywords:	Hydroforming, real time stereo computing, camera calibration, Snell law, transparent window.
Type:	Short Paper
First Page:	462
Last Page:	466
Language:	English
Cover:
Full Contents:	click to dowload
Paper Abstract:	Hydroforming is the process where a sheet metal workpart is formed by means of a high pressurized liquid. In order to avoid ruptures and to control the deformation, both internal pressure and material feeding towards the expansion zones have to be controlled during the forming stage. Process control is rather complicated. Thus, numerical modelling is widely used to define accurate tool shapes and to optimise process parameters. At the same time strain analysis techniques are often used to determine the material forming limits (by means of the so-called Forming Limit Diagram). These diagrams are also later used in numerical simulation to determine how far of the material limits is the part formed. Recently, CCD cameras have been used in order to obtain the FLD and dynamical records of the deformation of a particular part in real time. In order to obtain it, a regular known grid pattern (usually a dot-pattern) is electromechanically marked in the flat sheet before deformation. By means of CCD cameras and using stereovision techniques, the 3D coordinates of the grid points are obtained; meanwhile the part is deformed allowing one to obtain the real deformation state. In order to perform stereovision, using two or more CCD cameras, a camera calibration has to be made to obtain the function that relates the coordinates of the observed points in the world frame, to their projections in the image camera (measured in pixels).. However, in hydroforming processes, CCD cameras have to be usually protected by a transparent window. The observed points, as they are located on the other side of the transparent window, change the location relative to a direct observation (without window). This modification of the observation is due to the refraction (Snell law), and depends on the material of the window (relative speeds of light transmission), thickness and perpendicular vector of the window plane. In this paper, we present a computational scheme to do real time stereo computation of a regular grid pattern, observed by a couple of CCD cameras located on the other side of a transparent window. These results can thus be applied no only to hydroforming, but to any stereo calculation where cameras should be protected by a transparent window.
	Go Back