Positioning accuracy evaluation and corrective adjustment of reconfigurable assembly fixtures based on geometric constraints

Reconfigurable assembly fixtures (RAF) are prone to positioning accuracy degradation that impairs the assembly quality of products and thus it is necessary to implement effective monitoring of the positioning accuracy of such fixtures. The traditional manual inspection has deficiencies such as the inability to accurately evaluate the positioning accuracy of the fixture and the lack of corrective adjustment methods. To address these issues, this paper proposes a systematic and effective method for positioning accuracy evaluation and corrective adjustment of RAF based on geometric constraints. In terms of positioning accuracy evaluation, the method first analyzes the geometric constraint set required to ensure qualified fixture positioning accuracy, then constructs a geometric constraint-based evaluation model to quantitatively assess the fixture's positioning accuracy. For fixture corrective adjustment, the method calculates the adjustment amounts of key points using a point adjustment model, thereby determining the target adjustment positions of points and the specific locators needing adjustment. Meanwhile, a Jacobian-Torsor model is established to characterize the assembly deviations of locators, based on which, the adjustability of each locator is evaluated, providing guidance for workers to complete the fixture's corrective adjustment. The proposed method is validated on a reconfigurable assembly fixture for aircraft panels. Experimental results show that the method can accurately evaluate the fixture's positioning accuracy, repair the fixture and restore its positioning accuracy, thus verifying the feasibility and effectiveness of the proposed approach.