Determining Fixturing Points for Complex Objects

This paper presents a method to design fixtures for complex objects in robotized environments. The object is described with a set of points on its surface. First, an initial formclosure fixture is found with an iterative algorithm. The initial fixture is then improved with an iterative approach relying on a geometrical reasoning that efficiently looks for a locally optimum fixture; the quality of the fixture is measured considering the largest perturbation wrench that the fixture can resist, with independence of its direction. Once a locally optimum fixture has been reached, independent contact regions are computed to provide robustness in front of the locator positioning errors or to allow variations in the locators position. The proposed approach can also be applied to compute fixtures when one or several locators are fixed beforehand. The procedure has been implemented and application examples are included in the paper.