160 research outputs found
Constructing minimum deflection fixture arrangements using frame invariant norms
This paper describes a fixture planning method that minimizes object deflection under external loads. The method takes into account the natural compliance of the contacting bodies and applies to two-dimensional and three-dimensional quasirigid bodies. The fixturing method is based on a quality measure that characterizes the deflection of a fixtured object in response to unit magnitude wrenches. The object deflection measure is defined in terms of frame-invariant rigid body velocity and wrench norms and is therefore frame invariant. The object deflection measure is applied to the planning of optimal fixture arrangements of polygonal objects. We describe minimum-deflection fixturing algorithms for these objects, and make qualitative observations on the optimal arrangements generated by the algorithms. Concrete examples illustrate the minimum deflection fixturing method. Note to Practitioners-During fixturing, a workpiece needs to not only be stable against external perturbations, but must also stay within a specified tolerance in response to machining or assembly forces. This paper describes a fixture planning approach that minimizes object deflection under applied work loads. The paper describes how to take local material deformation effects into account, using a generic quasirigid contact model. Practical algorithms that compute the optimal fixturing arrangements of polygonal workpieces are described and examples are then presented
Frictionless grasp with 7 fingers on discretized 3D objects
This paper presents an algorithm to plain locally frictionless grasp on 3D objects. The objects can be of any arbitrary shape, since the surface is discretized in a cloud of points. The planning algorithm finds an initial force-closure grasp that is iteratively improved through an oriented search procedure. The grasp quality is measured with the “largest ball” criterion, and a force-closure test based on geometric considerations is used. The efficiency of the algorithm is illustrated through numerical example
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Automatic design of 3-d fixtures and assembly pallets
This paper presents an implemented algorithm that automatically designs fixtures and assembly pallets to hold three-dimensional parts. All fixtures generated by the algorithm employ round side locators, a side clamp, and cylindrical supports; depending on the value of an input control flag, the fixture may also include swing-arm top clamps. Using these modular elements, the algorithm designs fixtures that rigidly constrain and locate the part, obey task constraints, are robust to part shape variations, are easy to load, and are economical to produce. For the class of fixtures that are considered, the algorithm is guaranteed to find the global optimum design that satisfies these and other pragmatic conditions. The authors present the results of the algorithm applied to several practical manufacturing problems. For these complex problems the algorithm typically returns initial high-quality fixture designs in less than a minute, and identifies the global optimum design in just over an hour. The algorithm is also capable of solving difficult design problems where a single fixture is desired that can hold either of two parts
Development of Procedures for Accurate Finite Element Modeling of the Dynamic and Quasi-Static Performance of Automotive Chassis Components Incorporating Hyperelastic Materials
Finite element models of the vehicle for crashworthiness have traditionally included simplified representations of isolators intended to improve noise and vibration. However, the low stiffness of the hyperelastic material employed in such components allows for large deformations under impact conditions with a significant effect upon the accelerations experienced by the occupant. Modeling these components is challenging due to the non-linear behaviour of the material and the large deformations. The purpose of this research was to identify practices for developing accurate and efficient finite element models of chassis components incorporating hyperelastic materials. To maximize the comprehensiveness of this process, this research included quasi-static and dynamic material characterization; material model selection and implementation; finite element modeling techniques; quasi-static and dynamic component characterization; and model validation. Conclusions included the importance of comprehensive material characterization, material model selection, variation in results due to solver updates, and methodologies for model validation through component characterization
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