Algorithms, models and metrics for the design of workholding using part concavities.

摘要

In manufacturing, assembly and inspection, the term "workholding" refers to the tooling and processes required to hold parts in place. Workholding includes both grasping and fixturing. Grasping generally refers to holding a part with a robotic end-effector, primarily for moving it, and fixturing refers to holding a part on a rigid base using clamps and other elements primary for machining, painting, or welding. The results in this thesis apply to both grasping and fixturing: we will emphasize grasping in chapters III, IV, VI and VII, and fixturing in chapter V.; Workholding must align and accurately hold parts. The algorithmic design of workholding for rigid parts has been studied in detail for contact at part edges. In this dissertation, we consider workholding using contacts at concavities for rigid and deformable parts, and the algorithmic design and planning of workholding. Using concavities gives the advantages of self-alignment of the part to the fixture, and higher accuracy in part orientation, as concavities generally correspond to precise datum points. For deformable parts, concavities can be created or existing concavities accentuated to hold the part.; We study and propose models, metrics and algorithms for the design of workholding by starting with rigid parts and extending the results and analysis to deformable parts. We first identify exact solution sets of candidate workholding configurations and then use approximate methods to design one or more fixtures for a given part. Our workholding design process thus consists of first determining criticalities in part geometry using computational geometric methods, followed by numerical and heuristic procedures that evaluate candidate workholding configurations that lie within the bounds of the criticalities based on numerical approximations. To this end, we propose new workholding hardware and mathematical models to back the hardware. Based on the hardware, we also derive metrics and formal conditions for workholding.; We begin by studying rigid two-dimensional polygonal parts held on a horizontal plane held by a pair of vertical cylindrical jaws, with the jaws engaging part concavities. We call this new class of grips 2D v-grips . For 2D v-grips, we represent the distance between the jaws as a function of positions of the jaws along the perimeter, and prove the equivalence of immobility of the part and extrema of the distance function under conditions of concavity at the points of contact. (Abstract shortened by UMI.)