Inspired by analysis performed for the Space Shuttle External Tank Door uplatch mechanism, the goal of this work is to optimize a redundant path planar mechanism to equalize the force supported by each of its paths. Based on previous work which studies the behavior of split path transmissions, load sharing is found to be a ratio composed of path segment equivalent stiffnesses. To determine the equivalent stiffness of each load path segment, a finite element elastic linkage method is used to find mechanism deflection under load at a given configuration. This allows for the development of a routine which analytically computes load ratios based on a set of linkage cross sectional parameters. If link lengths and connectivity are selected to give a desired mechanism motion, a gradient based constrained nonlinear optimization algorithm is used to vary linkage cross sectional characteristics to find a solution which gives equal load sharing at a configuration of interest. Additionally, the same optimization algorithm is used to find the design which will accomplish this with the least RMS deviation from nominal dimensions. As well as minimizing these dimensional changes, the dimension of the design space is reduced using sensitivity analyses to identify links of greatest influence. These links are then given variable cross sections while all others remain fixed. To demonstrate this procedure, a set of two four-bar linkages whose cranks are connected by a torque tube is analyzed as a test case. Following the test case, the same procedures are used to analyze and optimize the uplatch mechanism geometry. Because this method of optimization is not specific to the uplatch mechanism, it may also be applied to other redundant path mechanisms which exhibit load sharing behavior.

Mike Tosto received a B.S. in mechanical and aerospace engineering from Cornell University in 2006. As an undergraduate, he worked on biologically inspired passive dynamic walking robots. Mike is currently an M.S. student in mechanical and aerospace engineering at the National Institute of Aerospace through the University of Virginia, and plans to graduate in May 2008.