A dual cam system for four-bar motion generation with adjustable length crank and follower links

Abstract

The objective in planar four-bar motion generation is to calculate the linkage dimensions required to achieve a group of prescribed coupler positions. For a given planar four-bar motion generator however, the rolling motion of its moving centrode over its fixed centrode will replicate its coupler motion. The curvature of the fixed and moving centrodes can be incorporated as contact surfaces in a rolling cam system to replicate the coupler motion of a planar four-bar motion generator. While the advantages that cam-based systems have over four-bar linkage-based systems are application-specific, some of the advantages relate to system workspace (having a more compact design), structural soundness (having a greater load bearing capacity) and design simplicity (utilizing fewer components). While design methods for cam-based systems have been developed for conventional non-adjustable four-bar motion generators, no such method has been presented for the adjustable planar four-bar motion generator. Given the design advantages associated with cam-based systems along with an absence of published work in the design of cam-based systems for adjustable motion generation, an opportunity exists to contribute to the body of knowledge in this area. This work presents for the first time a design method for a dual cam system to replicate the coupler motion of an adjustable planar four-bar motion generator. This design method incorporates an optimization model for defect-free adjustable planar four-bar motion generation. The adjustments considered in the optimization model are adjustable crank and follower moving pivots with adjustable crank and follower link lengths. This design method also incorporates centrode generation equations for the adjustable planar four-bar motion generator. As an example, the centrodes generated for a calculated adjustable motion generator were incorporated into a computer-aided design model to produce a concept dual cam system.

Keywords

• motion generation
• centrode generation
• planar linkage
• four-bar linkage
• adjustable linkage
• cam design