Optimal synthesis of force-generating planar four-link mechanisms

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Virginia Tech


This thesis presents a technique for the optimal synthesis of planar four-bar linkages for specified force or torque generation.

Unlike most previous research in mechanism force synthesis, this thesis targets linkage applications for which the mechanical advantage is prescribed but the position function is not. The advantage of this approach is that emphasis is placed on the force-generating properties of the linkage and not the output positions of the mechanism.

Closed-form synthesis of force-generating linkages based on Burmester theory has recently been developed in detail. Unfortunately, closed-form methods can only be used to solve a limited class of problems and frequently require substantial intuition on the part of the designer in adjusting the input parameter specifications. The approach presented here uses optimization theory to search a solution space for the mechanism that most nearly meets the designer's specification. Use of optimization allows a greater number of constraints to be applied to the synthesis such that more practical solutions can be obtained. The proposed design technique seeks to minimize an objective function that depends primarily on the force generation properties of the linkage and secondarily on the other applied constraints.

As a demonstration of the theoretical method, the optimal linkage synthesis technique is applied to a specific problem, namely, the design of a linkage for a weight-loaded exercise machine. Example solutions are generated and evaluated against the design constraints and mechanical advantage requirements. The design methodology presented has been implemented into a software package which is currently being used in industry for the design of similar linkages.



synthesis, mechanism, Optimization, linkage, force-generation