The quality of fixtures plays an important role in product quality during manufacturing,measuring or assembly. Finding methods for evaluating a fixture’s quality, which maydepend on workpiece errors, fixture errors, influences of clamping force, friction, etc.,is necessary to improve the product quality. This paper proposes the indicators that areused for estimating the quality of a fixture based on workpiece localizationrepeatability. Here, the workpiece localization will be considered in the followingdifferent cases: (1) considering only the influence of different geometric parameters(types) of the fixture, (2) taking into account the clamping force in the different typesof the fixture, (3) the influence of friction on the contacts of the workpiece-fixture. Afixture model is presented and analysed with some examples. An experimental fixture andworkpiece are then used to analyse and compare with the theoretical results.

Many object surfaces involve a number of pieces, expressed by different equations. Previous methods of optimal grasp planning can hardly cope with such cases. Ding et al. solve this problem by characterizing the object surface with convex facets and discrete points, then selecting the eligible ones for force-closure, and finally seeking the optimal contact positions on the selected elements. So far, however, no point contact with friction (PCwF) but only frictionless point contacts (FPC) can be used on the facets, while soft finger contacts (SFC) are excluded at all. In this paper, to the above two surface elements we add line segments. Moreover, the limitations on the contact types are completely removed. A general condition and a quantitative criterion of eligibility are presented, followed by a heuristic algorithm and an iterative algorithm for finding the better eligible elements. Three common examples show: the new advances make the formerly tough problems smoothly solvable.

Un montage d'usinage est un outillage indispensable pour fixer la pièce solidement à la bonne position dans l'espace de travail de la machine outil. La conception du montage d'usinage joue un rôle important pour obtenir une pièce usinée de bonne qualité. Nous avons déjà formalisé les connaissances sur les prises de pièce de manière à pouvoir les gérer tout au long du processus de conception de la gamme d'usinage. Maintenant nous nous intéressons à la conception du montage d'usinage de manière à passer du modèle prise de pièce retenu à la solution technologique qui sera utilisée sur le poste de travail. Cet article aborde le problème de conception du montage d'usinage modulaire du point de vue technologique dans sa globalité ; c'est-à-dire le choix et le placement des éléments technologiques en tenant compte de toutes les contraintes de qualité, d'accessibilité et de comportement mécanique du système pièce-montage d'usinage-outil de coupe durant l'usinage.