Modeling and analysis of conformability and static stability in flexible fixturing.

摘要

A conformable fixturing system removes the major bottleneck to implementation of fully agile and flexible machining lines. Suitable metrics are required to quantify how well a flexible mechanical work-holding device conforms to an arbitrary workpiece geometry. In addition to conforming to a part family, an effective flexible work-holding device must ensure stable equilibrium during machining, assembly or manipulation, and also minimize part feature error due to elastic deformation of its structural components.; This thesis presents a model to predict the effect of fixture-workpiece conformability on static stability in flexible workholding. Metrics to quantify the conformability between an arbitrary workpiece and the conformable fixture/grasp are developed. The model is experimentally verified using a pin-array type flexible fixture and is further used to analyze the effects of global and local conformability on fixture/grasp static stability for compliant parts.; The thesis also presents a model for part feature tolerance-based stiffness optimization of machining fixtures. The model enables determination of the optimal fixture stiffness required to keep the contribution of fixture elastic deformation to the total part feature tolerance less than a pre-determined value. Experimental data taken from a pin-array type flexible machining fixture is used to validate the model. Finally, use of the conformability-stability model and the tolerance-based stiffness optimization model for optimal synthesis of pin-array type flexible machining fixtures is discussed.