Design of deployable structures using limit analysis of partially rigid frames with quadratic yield functions
The linear programming approach to generating deployable structures is extend to allow a hinge rotating around an axis in arbitrary direction. Plastic limit analysis problem with quadratic yield function with respect to member-end moments is solved to generate hinges in arbitrary directions of a partially rigid frame. The directions of hinges are obtained from the member-end momemts along the local axes. Using the proposed method, three-dimensional mechanisms and deployable structures with small number of hinges are successfully obtained. The manufacturability of a deployable structure is confirmed by assembling a small-scale model.
Linear programming approach to design of spatial link mechanism with partially rigid joints
A simple systematic approach is presented for designing a spatial link mechanism with partially rigid joints. A linear programming (LP) problem to find an infinitesimal mechanism that maximizes the output displacement is first formulated. The objective function of this LP problem has a penalty term to obtain a sparse solution including small numbers of hinges and members to be removed. It is shown that the dual of this LP problem can be regarded as a plastic limit analysis problem that maximizes the load factor under the equilibrium condition and upper- and lower-bound constraints on the member-end forces of a given frame structure. A heuristic approach is presented to obtain a finite mechanism by solving the LP problem after updating the nodal locations in the direction of inextensional deformation. It is shown in the numerical examples that various planar and spatial mechanisms can be easily found using the proposed method.
New approach to vision-based BGA package inspection
Ball grid array (BGA) techniques have developed very fast due to the advantages of more I/O ports, small size, and so on. In this paper, a vision-based algorithm for BGA package inspection is proposed to accurately estimate center and diameters of solder-balls of BGA packages, so that defects of BGA packages, such as missing or extra balls, oversize or undersize balls, over-height or under-height balls, and pitch can be detected for ensuring the quality of BGA packages.