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This paper addresses methods for determining the motion of an elastically suspended rigid body in frictional contact at multiple distinct locations. The methods developed assume that: (1) The motion of the support from which the body is suspended and the elastic behavior of the suspension are known; (2) inertial forces are negligible (motion is quasi-static); and (3) the contact is characterized by Coulomb friction. The derived coupled set of spatial rigid body equations is used to determine both the unknown direction of the friction force (at each point of contact) and the unknown motion of the rigid body. The uniqueness of the set of active constraints when considering multipoint contact is also addressed. We show that, for any passive compliant system, if the coefficient of friction at each contact is upper bounded, the set of active constraints is unique. A procedure to determine both the set of active constraints and the motion of the constrained body is provided. [DOI: 10.1115/1.2098878]

Spatial elastic behavior is characterized by a 6X6 positive definite matrix, the spatial stiffness matrix, or its inverse, the spatial compliance matrix. Previously, the structure of a spatial stiffness matrix and its realization using a parallel elastic system have been addressed. This paper extends those results to the analysis and realization of a spatial compliance matrix using a serial mechanism and identifies the duality in spatial stiffness and compliance associated with parallel and serial elastic mechanisms. We show that, a spatial compliance matrix can be decomposed into a set of rank-1 compliance matrices, each of which can be realized with an elastic joint in a serial mechanism. To realize a general spatial compliance, the serial mechanism must contain joints that couple the translational and rotational motion along/about an axis. The structure of a spatial compliance matrix can be uniquely interpreted by a 6-joint serial elastic mechanism whose geometry is obtained from the eigenscrew decomposition of the compliance matrix. The results obtained from the analysis of spatial compliant behavior and its realization in a serial mechanism are compared with those obtained for spatial stiffness behavior and its realization in a parallel mechanism. [DOI: 10.1115/1.1434273]

Byline: Dewi Rahardja, Yan D. Zhao, Shuguang Huang Car manufacturers often need to compare and choose a car hood fixture that gives a good quality fitting between the hood and the body. The good quality hood fitting is usually defined as a constant-width gap between the hood and the body, and the quality is typically evaluated from CMM measured data collected from the hood edge after placement. In this paper, we propose a method to choose the best fixture. We conclude from simulations that the method are useful for car manufacturers to assess, compare, and choose the best car hood fixture that can meet their desired standard benchmark.

Previously, we have shown that, to realize an arbitrary spatial stiffness matrix, spring components that couple the translational and rotational behavior along/about an axis are required. We showed that, three such coupled components and three uncoupled components are sufficient to realize any full-rank spatial stiffness matrix and that, for some spatial stiffness matrices, three coupled components are necessary. In this paper, we show how to identify the minimum number of components that provide the translational-rotational coupling required to realize an arbitrarily specified spatial stiffness matrix. We establish a classification of spatial stiffness matrices based on this number which we refer to as the 'degree of translational--rotational coupling' (DTRC). We show that the DTRC of a stiffness matrix is uniquely determined by the spatial stiffness mapping and is obtained by evaluating the eigenstiffnesses of the spatial stiffness matrix. The topological properties of each class are identified. In addition, the relationships between the DTRC and other properties identified in previous investigations of spatial stiffness behavior are discussed.